Iron Deficiency Anemia

Iron deficiency anemia (IDA) is a microcytic hypochromic anemia resulting from insufficient iron stores to support normal erythropoiesis.

Also Called / Synonyms

• Iron deficiency anemia (IDA)
• Hypochromic microcytic anemia (shared with other microcytic anemias; specify iron-deficient)
• Sideropenic anemia (historical term, from Greek sideros for iron)
• Iron-deficiency erythropoiesis when referring to the stage before frank anemia

Stages of Iron Deficiency (Definition of Terms)

Iron deficiency progresses through three sequential stages before anemia appears. Laboratory thresholds are standard and guide clinical interpretation:

Ferritin is the earliest and most specific marker of iron stores in the absence of inflammation. Transferrin saturation (TSAT) and total iron-binding capacity (TIBC) become abnormal in the latent stage ^[6]B3b.

Classification by Severity (WHO Grading)

IDA is graded by hemoglobin (Hb) decrement, which guides the urgency of intervention:

• Mild: Hb 10-12 g/dL (women) or 11-13 g/dL (men)
• Moderate: Hb 7-10 g/dL
• Severe: Hb <7 g/dL Severe IDA can cause high-output heart failure , cognitive impairment in older adults ^[5]B2b, and increased perioperative risk ^[2]B2a.

Clinical Significance

IDA is the most prevalent anemia worldwide. In Iran, an umbrella meta-analysis estimated prevalence at 15.71% in pregnant women and 19.91% in children under six years ^[3]A1a. In older surgical cohorts, 26.7% of patients presenting for elective surgery were anemic, with the majority having mild-to-moderate IDA ^[5]B2b. IDA is also an independent marker of underlying pathology: prospective pan-endoscopy studies found potential bleeding lesions in 71.1% of patients with IDA, most commonly in the small bowel ^[4]B2b. The condition associates with chronic daily headache (51% of headache patients had IDA) ^[6]B3b and with celiac disease (adjusted hazard ratio 1.79) ^[7]B2b.

Because IDA is nearly always a manifestation of an underlying disorder, chronic blood loss, malabsorption, or increased demand, rather than a primary disease, its nomenclature includes the causal context. The pathophysiology that links iron depletion to impaired erythropoiesis is detailed in the next section.

Pearl: IDA is the most prevalent anemia globally and is typically a marker of an underlying condition (e.g., gastrointestinal bleeding, celiac disease) that requires investigation.

Building on the classification above, iron deficiency anemia (IDA) arises from a fundamental disruption of iron homeostasis governed by the hepcidin-ferroportin axis. Hepcidin, a liver-derived peptide hormone, is the central regulator: it binds to ferroportin on enterocytes, macrophages, and hepatocytes, triggering internalization and degradation of the iron exporter, thereby blocking dietary iron absorption and iron release from storage sites. In IDA, low iron stores suppress hepcidin expression, allowing ferroportin to remain active and augment iron absorption, a homeostatic response that becomes maladaptive when dietary supply or stores are insufficient to match demand.

The Hepcidin-Ferroportin Axis and Its Regulation

Hepcidin transcription is controlled by the BMP6 -hemojuvelin (HJV)-SMAD1/5/8 signaling pathway. Circulating iron and BMP6 bind to a receptor complex including HJV, activating SMAD phosphorylation, which translocates to the nucleus to drive hepcidin expression. The transmembrane serine protease matriptase-2 (encoded by TMPRSS6) acts as a negative regulator of this pathway by cleaving membrane-bound HJV, thereby reducing SMAD signaling and suppressing hepcidin ^[12]D5[13]D5. This negative-feedback loop ensures tight homeostatic balance: iron deficiency induces matriptase-2 activity, which lowers hepcidin; iron repletion removes this repression ^[13]D5[16]D5. Conversely, loss-of-function TMPRSS6 mutations lead to inappropriately elevated hepcidin, causing iron-refractory iron deficiency anemia (IRIDA) ^[12]D5[21]C4.

Stages of Iron Deficiency

Iron deficiency progresses through three stages: (1) iron depletion, low ferritin but preserved hemoglobin; (2) iron-deficient erythropoiesis, falling transferrin saturation and rising soluble transferrin receptor ; (3) frank IDA, hemoglobin drops, microcytosis and hypochromia emerge. In chronic inflammation ( anemia of chronic disease , ACD), hepcidin is upregulated by IL-6 via STAT3 signaling, and iron retention in macrophages is sustained even as systemic iron falls ^{[15]B3b[20]D5}. Phlebotomy or dietary iron restriction can suppress inflammation-driven SMAD1/5/8 phosphorylation, demonstrating that iron deficiency can overrule inflammatory hepcidin signals, but through distinct mechanisms depending on the mode of deficiency ^[20]D5.

Cellular and Vascular Consequences of Iron Deficiency

Low intracellular iron in bone marrow megakaryocyte-erythroid progenitors (MEPs) attenuates ERK1/2 signaling, slows proliferation, and biases lineage commitment toward megakaryocytes rather than erythrocytes, explaining the well-documented thrombocytosis seen in IDA ^[10]D5[14]D5. This bias is reproduced in Tmprss6-/- mice and in human MEPs after transferrin receptor 2 knockdown ^[14]D5. At the vascular level, iron deficiency reduces endothelial holo α-globin, liberating nitric oxide (NO) from its scavenger, thereby increasing NO bioavailability and promoting vasodilation, a mechanism that is sex-dependent in mice (observed in females but not males)^[9]D5. These NO-driven effects may contribute to the cardiovascular manifestations seen in severe IDA.

Genetic Forms: Iron-Refractory Iron Deficiency Anemia (IRIDA)

IRIDA is an autosomal recessive disorder caused by biallelic mutations in TMPRSS6 , leading to absent or nonfunctional matriptase-2. Unopposed BMP6 -HJV signaling results in persistently high hepcidin levels, dietary iron malabsorption, and partial responsiveness to parenteral iron ^[12]D5[21]C4. Affected individuals present in childhood with severe microcytic hypochromic anemia, inappropriately normal-to-elevated hepcidin, and low circulating soluble HJV ^[22]D5. Heterozygous TMPRSS6 variants also modify penetrance of HFE - hemochromatosis , attenuating iron overload ^[16]D5.

Other Trace Element Dysregulation

Pediatric IDA is accompanied by broader trace-element disturbances: serum zinc and magnesium are significantly lower, while copper is elevated, compared with controls ^[24]B2a. Whether these changes are consequences of shared dietary deficiencies or independent contributors to hematopoiesis remains unclear, but they underscore the nutritional complexity often underlying IDA.

These molecular insights set the stage for understanding the multifactorial origins of iron deficiency, from dietary insufficiency and blood loss to malabsorptive states and genetic blocks, which are detailed in the next section.

Pearl: Genetic defects in TMPRSS6, disrupting matriptase-2-mediated hepcidin suppression, cause iron-refractory iron deficiency anemia (IRIDA) with characteristic high hepcidin levels.

From the pathophysiologic understanding of hepcidin -mediated iron regulation and malabsorption, the epidemiologic profile of iron deficiency anemia (IDA) emerges with distinct patterns across populations and geographies.

Global Burden and Demographics

In 2010, global anemia prevalence was 32.9%, accounting for 68.36 million years lived with disability (95% UI 40.98-107.54), or 8.8% of total disability from all conditions ^[30]B2c. South Asia and Central, West, and East sub-Saharan Africa bear the highest burden, while East, Southeast, and South Asia saw the greatest prevalence reductions from 1990 to 2010 ^[30]B2c. Anemia prevalence dropped for both sexes over that period, though more for males ^[30]B2c. Females have higher prevalence in most regions and age groups ^[30]B2c; IDA affects nearly one-third of women globally, with heavy menstrual bleeding a leading contributor ^[36]B2c. Children under 5 years carry the highest burden and were the only age group with a negative trend (increasing prevalence) from 1990 to 2010 ^[30]B2c.

Etiologic Drivers

IDA arises from insufficient dietary iron, impaired absorption, or chronic blood loss. The World Health Organization recommends universal iron supplementation in high-prevalence settings, though a large placebo-controlled trial in 3300 Bangladeshi infants found no cognitive benefit at 3 months from iron syrup or multiple micronutrient powders despite improvements in hematologic markers ^[29]A1b. In adults, the most common acquired cause is blood loss: gastrointestinal bleeding, heavy menstrual bleeding, and iatrogenic sources such as anticoagulation. Direct oral anticoagulants ( DOACs ) - particularly rivaroxaban - are associated with a 2.7-fold higher risk of abnormal uterine bleeding compared with LMWH/vitamin K antagonists (RR 2.68) ^[32]A1a, a risk that may be underestimated when relying on standard bleeding criteria ^[32]A1a.

Risk Factors

Several demographic, genetic, and procedural factors substantially increase IDA risk. Bariatric surgery is a growing cause: in a retrospective cohort, 43% of patients developed iron deficiency and 16% IDA over a mean 31 months of follow-up, with malabsorptive procedures more than doubling risk (HR 1.92) ^[31]B3b. Baseline anemia conferred a strikingly elevated hazard for IDA (HR 19.6), and low baseline ferritin (HR 0.96 per ng/mL) and young age (HR 0.90 per year) were additional predictors ^[31]B3b. After laparoscopic sleeve gastrectomy , female sex (OR 3.660, 95% CI 1.676-7.995) and preoperative anemia were independent risk factors, while higher iron saturation was protective (OR 0.914, 95% CI 0.887-0.942) ^[42]B3b.

In West African children, the TNF(-308) AA genotype conferred an adjusted odds ratio of 8.1 for iron deficiency and 5.1 for IDA following the malaria season, an effect likely mediated by TNF-α-induced inhibition of intestinal iron absorption ^[35]B3b. The prevalence of IDA increased significantly over the malaria season (P < 0.001) ^[35]B3b, illustrating seasonal variation in endemic areas.

Autoimmune gastritis (AIG) is an underrecognized cause; anemia occurs in 39.3% of AIG patients, of whom 17.9% have IDA and 21.4% pernicious anemia ^[43]B3b. Intrinsic factor antibody positivity was a significant risk factor for anemia (OR 2.379, P = 0.047), and H. pylori infection was more prevalent in AIG patients with IDA than in those with pernicious anemia (66.7% vs 28.0%, P = 0.009) ^[43]B3b, linking infection to an iron-deficient phenotype.

Table: Risk factors for iron deficiency anemia identified from cohort and genetic studies.

These risk factors highlight populations warranting targeted screening and earlier intervention. The patterns of age, sex, geographic location, and comorbid conditions that predispose to IDA set the stage for its clinical recognition. The following section translates these epidemiologic clues into the signs and symptoms that prompt laboratory evaluation.

Pearl: The single strongest predictor of IDA after bariatric surgery is preoperative baseline anemia (HR 19.6); correcting it preoperatively may substantially reduce postoperative IDA burden ^[31]B3b.

The gradual decline in iron stores that begins with prelatent deficiency rarely produces symptoms; it is only once hemoglobin synthesis becomes impaired that the classic picture emerges. The presentation is shaped by the rate of progression, the depth of anemia, and the underlying cause.

Presenting Symptoms

The onset is insidious over weeks to months. Fatigue, weakness, exercise intolerance, impaired concentration, irritability, and depressed mood are common but nonspecific ^[53]D5. As hemoglobin falls, dyspnea on exertion and palpitations may appear. In pregnancy, IV iron therapy significantly improves fatigue and depression scores ^[50]C4.

Two distinctive symptoms merit specific inquiry. Pica, craving for non-nutritive substances (ice, clay, starch, bricks), is a classic manifestation; one case report describes a patient who developed an olfactory craving for bricks leading to ingestion ^[54]C4. Restless legs syndrome (RLS) is another key association; a variant can present as refractory shoulder pain rather than leg discomfort, and polysomnography shows an elevated Periodic Limb Movement during Sleep index ^[55]C4. In infants, universal iron supplementation improved later iron status but did not show an immediate effect on cognitive development scores ^[29]A1b.

Neurological Examination Findings

Neurologic findings are limited but distinctive. RLS is the most common manifestation: an irresistible urge to move the limbs, worsening at rest and in the evening, partially relieved by movement ^[55]C4. Cranial nerve and motor exams are typically normal. Pallor (conjunctival, palmar), glossitis, angular cheilitis, and koilonychias are physical signs of chronic iron deficiency.

Phenotypic Variants

Several clinical variants reflect the underlying etiology (Table 1).

Red Flags

• Hemoglobin <7 g/dL with cardiac ischemia, heart failure, or severe dyspnea → transfusion evaluation ^[33]D5.
• New-onset pica involving noxious substances (e.g., bricks) → urgent behavioral intervention and iron repletion ^[54]C4.
• IDA in adults ≥45 years without clear cause → bidirectional endoscopy for occult GI bleeding ^[51]B3b, ^[53]D5.
• Severe epistaxis or overt GI bleeding in known HHT → consider systemic therapy (e.g., pomalidomide) ^[44]A1b, ^[47]D5.
• Children with severe anemia → risk of neurologic complications and heart failure ^[46]D5.

Atypical Presentations

IDA may masquerade as other conditions. Variant RLS has been misdiagnosed as frozen shoulder when symptoms localize to the upper limb ^[55]C4. Iron deficiency without anemia can produce fatigue, cognitive complaints, and RLS despite normal hemoglobin; reliance on sex-specific reference ranges may miss the diagnosis in menstruating women ^[53]D5. Olfactory cravings leading to pica represent an underrecognized pathway ^[54]C4. IDA may be the first and only manifestation of autoimmune gastritis, particularly in women with autoimmune hypothyroidism and dyspepsia ^[52]B2b.

Pearl: When evaluating unexplained fatigue, check ferritin and transferrin saturation even if hemoglobin is low-normal, iron deficiency without anemia can cause significant symptoms ^[53]D5. In any adult with new IDA, the most common cause is occult gastrointestinal bleeding; a negative bidirectional endoscopy should prompt testing for celiac disease and Helicobacter pylori ^[53]D5.

The clinical suspicion raised by fatigue, pallor, and pica must now be confirmed by a diagnostic sequence that moves from the peripheral blood film to iron biomarkers and, in selected cases, to bone marrow examination and molecular testing. The goal is not only to document iron deficiency but also to identify its cause and exclude mimics such as thalassemia trait, anemia of chronic disease, and myelodysplastic syndromes (MDS).

Peripheral Blood Smear

The blood film in iron deficiency anemia (IDA) shows microcytic hypochromic red cells with anisopoikilocytosis, including pencil cells and occasional target cells. A characteristic finding is reactive thrombocytosis, present in up to one-third of patients. Mechanistically, low iron biases megakaryocyte-erythroid progenitors (MEPs) toward megakaryocytic commitment via attenuated ERK1/2 signaling, slowing proliferation and increasing platelet production ^[10]D5[14]D5. This thrombocytosis resolves with iron repletion. The smear also provides initial clues to alternate diagnoses: basophilic stippling suggests thalassemia or lead poisoning; fragmented cells point to microangiopathic hemolytic anemia.

Bone Marrow Examination

Bone marrow aspiration with Perls Prussian blue staining for storage iron is the gold standard for assessing total body iron stores. In IDA, stainable iron in macrophages and erythroblasts (sideroblasts) is absent or markedly reduced. This is particularly valuable when serum ferritin is equivocal (e.g., 30-100 μg/L) or when inflammation coexists. In a large series of 6,610 patients with hematologic disorders, ferritin showed the highest area under the curve for predicting reduced marrow iron (AUC 88% in females, 89% in males). A ferritin ≤30 μg/L was 97-99% specific for absent stores, but sensitivity was only 35-54% ^[60]B2b. Marrow examination is indicated when:

• Iron indices are discordant (e.g., low MCV but normal ferritin).
• The patient is refractory to oral iron therapy.
• There is suspicion of MDS (e.g., older age, macrocytosis, cytopenias).

In iron-refractory microcytic anemia, Perls staining may reveal ring sideroblasts (≥15% of erythroblasts), indicating impaired iron utilization rather than deficiency. Such cases warrant SF3B1 mutation testing to distinguish MDS with ring sideroblasts from other causes ^[25]C4.

Flow Cytometry and Molecular Profiling

Flow cytometry has a limited role in classic IDA but is used to evaluate unexplained cytopenias. In patients with thrombocytosis, immunophenotyping of MEPs can confirm a skewed megakaryocytic lineage ^[14]D5. More broadly, molecular testing targets the underlying etiology when iron deficiency is unexplained:

• Hepcidin measurement: Low hepcidin levels (<6.8 ng/mL in children, <4.5 ng/mL in women) support absolute iron deficiency and help differentiate IDA from anemia of chronic disease ^{[57]D5[62]B3b}. However, harmonized assays are still lacking.
• Zinc-protoporphyrin/heme ratio: A point-of-care biomarker; a ratio >90 μmol/mol heme in children (likelihood ratio 20.2) and >107 μmol/mol heme in women (likelihood ratio 10.8) diagnoses IDA with high confidence ^[62]B3b.
• Genetic testing: The VWF p.Tyr1584Cys variant increases odds of IDA (OR 1.55) and heavy menstrual bleeding, linking iron deficiency to von Willebrand disease ^[64]B3b. In children, TMPRSS6 mutations cause iron-refractory IDA (IRIDA), characterized by inappropriately high hepcidin.

Diagnostic Algorithm

All patients suspected of IDA should have a complete blood count , ferritin, transferrin saturation (TSAT), and a blood film. When ferritin is ≤30 μg/L, IDA is confirmed without marrow. For ferritin 30-100 μg/L, especially with inflammation, a marrow examination or hepcidin/ZPP testing may be needed. If marrow shows ring sideroblasts, SF3B1 sequencing is performed ^[25]C4. Once IDA is diagnosed, the workup must identify the cause: gastrointestinal evaluation (including bidirectional endoscopy for occult bleeding) and testing for celiac disease and Helicobacter pylori infection ^[53]D5.

Pearl: A ferritin >30 μg/L does not rule out iron deficiency in patients with hematologic disorders, only a ferritin >1,750 μg/L in females and >4,967 μg/L in males provides 95% negative predictive value for reduced marrow stores ^[60]B2b.

Once the diagnosis of iron deficiency anemia (IDA) is confirmed by laboratory testing, the evaluation shifts to stratifying disease severity, distinguishing physiologic subtypes, and identifying prognostic factors that guide management intensity and follow-up.

Severity Classification

IDA severity is traditionally graded by hemoglobin (Hb) concentration, though no universal thresholds are captured in the provided literature. Pragmatically, mild anemia (Hb 10-12 g/dL in women, 11-13 g/dL in men) rarely requires urgent intervention, whereas moderate (Hb 7-9.9 g/dL) and severe (Hb <7 g/dL) demand prompt treatment and investigation for underlying blood loss. A more granular severity classification specific to hereditary hemorrhagic telangiectasia (HHT), a common cause of chronic IDA, has been validated using the HHT-QoL scale: scores of 0 (no limitation), 1-3 (mild), 4-7 (moderate), and 8-16 (severe limitation) ^[1]C4.

Subtypes: Absolute vs. Functional Iron Deficiency

Iron deficiency anemia is not a single entity; the peritoneal dialysis literature illustrates a clinically important subclassification that has prognostic implications. Using transferrin saturation (TSAT) and ferritin levels, patients are grouped into:

• Absolute IDA: TSAT <20% + ferritin <100 ng/mL
• Functional IDA (FID): TSAT <20% + ferritin 100-500 ng/mL
• High-risk FID: TSAT <20% + ferritin >500 ng/mL ^[73]B2b

This high-risk FID phenotype, reflecting iron-restricted erythropoiesis despite adequate stores, likely driven by inflammation, carries a substantially worse prognosis ^[73]B2b.

Prognostic Factors

In the largest longitudinal cohort examining IDA outcomes (n=2,121 peritoneal dialysis patients), independent predictors of all-cause mortality include female sex (OR 1.29), reduced eGFR (OR 0.93 per unit decline), hypoalbuminemia (OR 2.19), and elevated hs-CRP (OR 1.68) ^[73]B2b. The high-risk FID group independently predicted all-cause mortality (HR 1.94, P=0.005) and cardiovascular mortality (HR 1.98, P=0.037) after full adjustment ^[73]B2b. In lung cancer patients with cancer-related anemia, a nomogram integrating serum iron, albumin, CRP, total cholesterol, KPS score, surgery, and chemotherapy achieved an AUC of 0.758 (training) and 0.760 (validation) for predicting anemia risk ^[70]B2b.

Risk Stratification in Special Populations

Pregnancy: TMPRSS6 variants (rs855791 T-allele, rs4820268 G-allele) are consistently associated with lower serum iron, reduced transferrin saturation, and elevated unsaturated iron-binding capacity, increasing the risk of IDA, gestational diabetes mellitus, and preeclampsia ^[71]B2a. Incorporating TMPRSS6 genotyping into prenatal care may allow personalized iron supplementation ^[71]B2a.

Athletes: Hepcidin-based screening, either serum hepcidin (AUC 0.85-0.90) or non-invasive urinary hepcidin/creatinine (AUC 0.85-0.88), can identify iron deficiency with sensitivities of 0.74-0.91 and specificities of 0.73-0.92 ^[74]C4. These tests may serve as triage tools to guide oral iron therapy before anemia develops.

Early-onset colorectal cancer : IDA itself is a significant risk marker; in a case-control study of adults 20-49 years, iron deficiency anemia was independently associated with higher odds of EOCRC (OR not isolated in abstract), reinforcing the need for endoscopic evaluation in young patients with unexplained IDA ^[51]B3b.

Pearl: The distinction between absolute and functional iron deficiency (especially high-risk FID with ferritin >500 ng/mL) identifies a subset of patients with sharply elevated mortality risk (HR ~1.94) ^[73]B2b; in such cases, addressing inflammation may be as important as iron repletion.

Staging and risk stratification (Section 6) have identified patients with severe, symptomatic iron deficiency anemia (IDA) who require urgent intervention. Acute management focuses on rapid hemoglobin (Hb) restoration while avoiding transfusion risks, guided by hemodynamic stability and the underlying cause.

Step 1: Initial Assessment and Severity Classification

Classify severity by Hb level and clinical status. Severe IDA is defined as Hb < 70 g/L (7 g/dL) ^[78]C4; life-threatening values may drop as low as 1.9 g/dL without immediate decompensation if anemia is chronic ^[81]C4.

• Hemodynamically unstable (hypotension, tachycardia, altered mental status, active bleeding): immediate need for transfusion.
• Hemodynamically stable: clinical status takes precedence over laboratory values ^[81]C4. Assess for causes: nutritional deficiency (children), menstrual bleeding, gastrointestinal pathology, or parasitosis (e.g., pediculosis in vulnerable populations ^[82]C4).
• Disposition: unstable patients go to the intensive care unit; stable patients can be managed in the emergency department or ward.

Step 2: First-Line Interventions for Stable Severe IDA

For hemodynamically stable patients, IV iron therapy is preferred over packed red blood cell (PRBC) transfusion ^[78]C4. Intravenous iron sucrose (IS) or ferric carboxymaltose (FCM) can rapidly raise Hb while avoiding transfusion-associated risks ^[78]C4.

• IV iron sucrose: In a pediatric emergency department cohort, 23% of severe IDA patients received IS; median time to increase Hb by 20 g/L was 7 days (95% CI 0.7-10.5 days) ^[78]C4. Doses follow institutional protocols (e.g., 200 mg total in the pediatric case report ^[81]C4).
• Ferric carboxymaltose: In a preoperative adult cohort, the median total dose was 1000 mg administered over a 5-day (IQR 0-16) period before surgery ^[77]B3b. Underdosing and insufficient time before surgery reduced effectiveness ^[77]B3b.

Both agents had no severe reactions and no returns to the emergency department for anemia within 30 days ^[78]C4.

Step 3: Transfusion Criteria and Administration

Reserve PRBC transfusion for patients with:

• Hemodynamic instability.

• Active bleeding.

• Life-threatening symptoms (e.g., syncope, heart failure).

• Inability to tolerate IV iron (rare).

• Dose: 10-15 mL/kg of PRBCs (based on pediatric data ^[81]C4). In adults, typically 1-2 units.

• Risk: Transfusion can cause transfusion-associated circulatory overload (TACO) and mild reactions; in one pediatric series, 1 of 16 transfused patients developed TACO ^[78]C4.

• Goal: Raise Hb to a safe level (e.g., >70 g/L) without aiming for full correction in the acute setting.

⚠ Warning: Avoid unnecessary transfusion in stable chronic anemia, the slow adaptation allows very low Hb tolerability, and transfusion adds risk without benefit ^[78]C4[81]C4.

Step 4: Monitoring and Response Assessment

• Post-IV iron: Recheck Hb and reticulocyte count at 2 weeks ^[78]C4. A rise of ≥ 20 g/L is expected within 7-10 days ^[78]C4.
• Post-transfusion: Monitor for signs of volume overload (TACO), especially in elderly or cardiac patients; from ^[76]B3b, preoperative IDA increases 30-day mortality (HR 1.91, 95% CI 1.22-2.98) and 365-day mortality (HR 2.78, 95% CI 2.13-3.62) compared to nonanemic patients ^[76]B3b.
• Check for cause: After stabilization, pursue diagnostic workup for gastrointestinal bleeding (e.g., colonoscopy , given IDA as a red-flag sign for colorectal cancer ^{[75]B3b[79]C4}), menstrual loss, or parasitosis ^[82]C4.

Step 5: Transition to Long-Term Management

Once the patient is stable and Hb is rising, transition to oral iron therapy for continued repletion. However, be aware of iron pill gastritis as a rare but serious adverse effect (case report of severe, Helicobacter pylori-negative gastritis with iron deposition after starting oral iron) ^[80]C4. Resolution occurs upon cessation ^[80]C4. Discharge planning should include follow-up for completion of iron stores and treatment of underlying etiology. This bridges to Section 8 (Long-term & Definitive Management).

Management Algorithm

Figure 1: Acute management of severe IDA (adapted from ^[78]C4[81]C4).

Dosing Overview

Note: Doses for iron sucrose are not standardized in the provided literature; local protocols should be followed.

Controversies and Guideline Disagreement

No major guideline disagreements were identified from the reviewed evidence regarding acute management of severe IDA. However, practice variation exists between early IV iron versus transfusion for stable patients; the available pediatric data support IV iron as a safe alternative ^[78]C4.

Pearl: In hemodynamically stable patients with severe IDA, intravenous iron therapy (sucrose or carboxymaltose) can safely achieve a rapid hemoglobin rise without exposing patients to the risks of transfusion (TACO, alloimmunization), but underdosing and delay reduce its effectiveness ^{[77]B3b[78]C4}.

Once severe anemia has been stabilized and the underlying cause identified, the goal shifts to fully restoring iron stores, normalizing hemoglobin, and preventing relapse. This requires a targeted strategy tailored to the patient's iron deficit, gut tolerance, ongoing losses, and comorbidities.

Step 1: Choose the Route of Iron Repletion

Oral iron remains first-line for uncomplicated iron deficiency anemia (IDA) ^[90]D5. Ferrous sulfate (60-200 mg elemental iron daily) is the most studied and least expensive option ^[45]A1b. A pilot randomized trial in pregnancy found that daily dosing achieves the best iron load, though adherence was lower (47%) than with alternate-day (62%) or thrice-weekly (61%) schedules ^[45]A1b. For most patients, daily oral iron is recommended to ensure adequate total dose delivery, with dose reduction or every-other-day dosing reserved for those intolerant to daily therapy. Newer formulations, ferric maltol, sucrosomial® iron, and liposomal iron, may reduce gastrointestinal side effects and, in meta-analysis of pediatric trials, liposomal iron produced a greater hemoglobin increase at 6 months (MD 0.96 g/dL, 95%) with fewer adverse events (RR 0.29) ^[87]A1a. Bovine lactoferrin, however, was inferior to ferrous sulfate in a Bangladeshi trial (Hb change -0.2 vs 1.1 g/dL) and should not be used as a substitute ^[88]A1b.

Intravenous iron is indicated when oral iron is ineffective, poorly tolerated, or when rapid repletion is needed, in ongoing blood loss, malabsorption (e.g., celiac disease, bariatric surgery), chronic kidney disease (CKD) on dialysis, or late pregnancy ^[56]D5[33]D5. In women with heavy menstrual bleeding (HMB), first-line IV iron dextran was cost-effective (incremental cost-effectiveness ratio $28 600 per QALY) compared with oral ferrous sulfate ^[36]B2c. Modern high-dose formulations allow complete repletion in one or two infusions. Ferric derisomaltose (FDI) is preferred over ferric carboxymaltose (FCM) because FCM causes hypophosphatemia and, in a cohort of 357 patients and validation in >20 000 TriNetX records, was independently associated with higher fracture risk ^[83]B3b. In hemodialysis patients, FCM 500 mg single dose increased hemoglobin by +0.50 g/dL at 4 weeks and was well tolerated ^[95]C4.

Red blood cell transfusion is reserved for hemodynamically unstable anemia or hemoglobin <7 g/dL (7-8 g/dL in hospitalized patients with acute coronary syndrome) ^[33]D5.

Step 2: Address the Underlying Cause

Long-term cure demands eliminating the driver of iron loss or malabsorption. In hereditary hemorrhagic telangiectasia (HHT), systemic antiangiogenic therapy (pomalidomide 4 mg daily, which reduced Epistaxis Severity Score by 0.94 points vs placebo, 95% CI -1.57 to -0.31) and antifibrinolytics are increasingly preferred over repetitive procedures ^{[44]A1b[47]D5}. For women on anticoagulation, particularly rivaroxaban (2.7-fold higher abnormal uterine bleeding risk than LMWH/VKA), switching to an alternative anticoagulant or managing HMB can prevent recurrent IDA ^[32]A1a. In celiac disease, strict gluten-free diet adherence improves iron status; IDA was present in 23.9% of children with CD and was more common with poor adherence ^[68]C4. When IDA is refractory to oral iron despite adequate intake, consider Helicobacter pylori infection, atrophic gastritis, or iron-refractory iron deficiency anemia (IRIDA) due to TMPRSS6 mutations, characterized by inappropriately high hepcidin and only partial correction with IV iron ^[91]D5.

Step 3: Monitor and Prevent Relapse

Recheck hemoglobin and ferritin 4-8 weeks after initiating therapy. A rise of ≥1 g/dL in Hb or reticulocyte hemoglobin equivalent (Ret‑He) increase of ≥1 pg predicts response ^[93]B2b. Once stores are replete (ferritin >50-100 μg/L), continue iron for an additional 2-3 months to replenish total body stores ^[56]D5. In patients with persistent blood loss (e.g., menorrhagia, anticoagulation, gastrointestinal angiodysplasia ), intermittent maintenance dosing (e.g., once or twice weekly) can prevent recurrence. Screening high-risk groups (premenopausal women, pregnant women, young children, vegetarians, post-bariatric surgery) with periodic ferritin measurement enables early re-intervention ^{[56]D5[66]A1c}.

Controversies and Guideline Disagreement

Pearl: For uncomplicated IDA, start daily oral ferrous sulfate (60-200 mg elemental iron); escalate to IV iron (preferably ferric derisomaltose) if oral fails, ongoing losses persist, or rapid correction is needed, and always pursue the underlying driver to prevent recurrence.

With long-term iron replacement established, the clinician managing IDA in the context of hematopoietic stem cell transplantation (HCT) or cellular therapy must navigate unique challenges: iron deficiency may coexist with the underlying hematologic disease, affect transplant logistics, and arise as a complication of transplant itself.

Iron Deficiency and Stem Cell Mobilization

Iron deficiency (with or without anemia) does not impair peripheral blood stem cell mobilization or colony-forming capacity. In a study of 102 children, peripheral blood CFU assays showed no significant difference between iron-deficient, iron-deficient anemic, vitamin B12-deficient, and control groups ^[99]B3b (3b). This supports the safety of collecting stem cell samples before correcting iron deficiency in emergent situations ^[99]B3b.

Step 1: Pre-Transplant Iron Assessment

All HCT candidates should undergo iron studies|iron deficiency screening (serum ferritin, TSAT, CBC) as part of pre-transplant evaluation. Iron deficiency is common in hematologic malignancies due to blood loss, poor intake, or disease-related inflammation (PMID:33667659) ^[98]D5 (5). Correcting IDA before conditioning reduces peri-transplant anemia and transfusion requirements.

Step 2: Iron Repletion in Transplant Candidates

• Mild-to-moderate IDA: Treat with oral ferrous sulfate 325 mg (65 mg elemental iron) once daily or every other day to optimize absorption and tolerability (standard dose).
• Severe IDA or intolerance: IV iron sucrose or ferric carboxymaltose is an alternative; doses follow standard protocols.
• Urgent stem cell collection: Do not delay harvest for iron repletion, stem cell yield is not compromised ^[99]B3b (3b).

Step 3: Iron Deficiency as a Complication of HCT

Graft-versus-host disease (GVHD), particularly gastrointestinal GVHD, causes mucosal ulceration and bleeding, leading to iron deficiency. Capsule endoscopy (CE) is a safe, well-tolerated tool for evaluating small-bowel GVHD and occult bleeding. In pediatric cohorts, CE yielded positive findings in 88% of cases evaluated for GVHD ^[100]C4 (4), and 26-44% of CE exams resulted in a change in therapy for IDA and obscure bleeding ^[101]C4 (4). CE should be considered in HCT recipients with unexplained IDA, especially when GVHD is suspected.

Step 4: Managing IDA in Transplant Recipients

Step 5: Iron Therapy During Cellular Therapy (CAR-T, Bispecific Antibodies)

Patients receiving CAR-T cells or bispecific antibodies may develop IDA from cytokine release syndrome (CRS)-related bleeding, prolonged hospitalization, or underlying disease. Oral iron is preferred if the gut is intact; IV iron is reserved for malabsorption or intolerance. No evidence indicates that iron supplementation interferes with CAR-T efficacy. The microbiome impact of these therapies is under investigation ^[98]D5 (5).

What NOT to Do

Do not withhold clinically necessary iron repletion out of concern for interfering with stem cell mobilization or engraftment, the evidence does not support such a concern ^[99]B3b (3b). Also avoid empiric iron therapy without confirming deficiency, as transplant patients are at risk for iron overload from transfusions.

Controversies and Guideline Disagreement

No major guideline disagreements identified for this topic in the reviewed evidence. The role of routine iron screening in all HCT candidates is not explicitly addressed by major transplant guidelines, but the low risk and potential benefit support inclusion in pre-transplant evaluation.

Pearl: Iron deficiency does not impair stem cell mobilization or colony-forming capacity; stem cell collection can proceed before iron repletion in urgent situations (PMID:29356316) ^[99]B3b. For HCT recipients with unexplained IDA, capsule endoscopy is a high-yield diagnostic tool, particularly when GVHD is suspected (diagnostic yield up to 88%) ^{[100]C4[101]C4}.

While hematopoietic cell transplantation is rarely indicated for iron deficiency anemia (IDA), the hematologist's role in managing IDA centers on three distinct axes: red blood cell transfusion support, anticoagulation strategy in the bleeding patient, and control of reactive thrombocytosis.

Step 1: Red Blood Cell Transfusion

Threshold: Restrictive transfusion (target hemoglobin 7-8 g/dL) is as safe as a liberal strategy (9-10 g/dL) in most clinical settings ^[33]D5 (level 5). Evidence is insufficient for acute coronary syndromes , heart failure, or high-risk coronary disease; here, transfusion should be guided by symptoms and patient preference ^[33]D5. For asymptomatic children with IDA and no active bleeding, packed red blood cell transfusion should be avoided (ASH-ASPHO Choosing Wisely) ^[109]A1c (level 1c). In obstetrics, per SOGC guidelines, transfusion is reserved for hemodynamic instability or severe anemia (Hb <6 g/dL) near delivery ^[66]A1c (level 1c).

Iron as the foundation: In stable patients without active bleeding, intravenous iron therapy is generally preferred over transfusion when urgent hemoglobin correction is not needed ^[33]D5 (level 5). For pregnant women with moderate IDA, IV iron (ferric carboxymaltose or ferric derisomaltose) produces more rapid improvement in reticulocyte indices and MCV compared with oral iron, but by 42 days postpartum indices converge ^[93]B2b (level 2b).

Step 2: Anticoagulation Strategy in the Bleeding Patient

Patients with IDA frequently require anticoagulation for VTE or atrial fibrillation . The choice of anticoagulant critically affects ongoing blood loss.

For women with VTE and heavy menstrual bleeding: DOACs overall do not significantly increase uterine major bleeding compared with LMWH/VKA (RR 1.47), but rivaroxaban carries a 2.68-fold higher risk of unspecified abnormal uterine bleeding ^[32]A1a (level 1a). Consider switching to apixaban , edoxaban , or a vitamin K antagonist if AUB persists and drives IDA.

For patients with hereditary hemorrhagic telangiectasia (HHT) and atrial fibrillation: Percutaneous left atrial appendage closure (LAAC) is recommended over long-term oral anticoagulation because HHT patients tolerate antiplatelet therapy poorly ^[112]B2a (level 2a). After LAAC, a simplified antiplatelet regimen (single aspirin for 3 months) is safe; device-related thrombus was absent in 57 patients analysed, despite only 12.3% tolerating prolonged DAPT ^[112]B2a.

For cerebral venous thrombosis (CVT) with IDA: Anticoagulation (LMWH followed by warfarin or DOAC) is mandatory ^[118]B2b (level 2b). Although IDA-CVT presents with more parenchymal lesions, 1-year outcomes are similar to non-IDA CVT (aOR for excellent outcome 0.60) ^[118]B2b. Concurrent iron replacement and treatment of the underlying cause (e.g., gynecological surgery, hormonal therapy) are essential to prevent recurrence.

Step 3: Cytoreduction - Addressing Reactive Thrombocytosis

IDA is frequently accompanied by reactive thrombocytosis, driven by iron's role in hematopoietic lineage decisions ^[116]D5 (level 5). Correction of iron deficiency normalizes the platelet count; cytoreductive agents are generally not indicated. Platelet count >1,000 × 10⁹/L is uncommon; thrombotic events are rare, and aspirin prophylaxis has not been studied specifically in this population. The primary treatment is oral or intravenous iron therapy.

What not to do: Do not administer platelet transfusion for asymptomatic thrombocytosis in IDA. Do not initiate cytoreductive drugs (hydroxyurea, anagrelide) for reactive thrombocytosis; they are unnecessary and expose the patient to myelotoxicity. Do not transfuse packed red blood cells for asymptomatic children with IDA ^[109]A1c.

Controversies and Guideline Disagreement

Pearl: Transfusion is reserved for symptomatic severe anemia; correct iron deficiency to resolve both anemia and reactive thrombocytosis; in patients with IDA requiring anticoagulation, choose agents with lower bleeding risk (avoid rivaroxaban in women with menorrhagia) and consider LAAC for HHT.

Having established that transfusion is reserved for unstable or severe anemia in the preceding section, the evolution of iron replacement therapy itself has undergone several paradigm shifts over the past five decades. Early practice focused solely on oral ferrous sulfate at a standard dose of 300 mg three times daily, based on the assumption that thrice-daily dosing maximized absorption. A landmark 1980 study in adults with iron-deficiency anemia demonstrated that this regimen did not cause serum ferritin to rise until hemoglobin normalized; by contrast, a double dose (600 mg three times daily) produced a transient ferritin spike within 2 days, reflecting iron absorption in excess of erythropoietic demand ^[119]C4. That observation hinted that absorption efficiency might saturate, challenging the rationale for high-frequency dosing.

From Oral Iron to Alternate-Day Dosing

In the 2010s, the recognition that hepcidin blocks iron absorption for roughly 24 hours after a dose prompted trials of alternate-day oral iron. A 2024 pilot randomized trial in pregnant women without anemia compared 200 mg ferrous sulfate daily, alternate days, or three times per week ^[45]A1b. Adherence was lowest in the daily arm (47%) versus 62% and 61% in the lower-frequency arms, yet the daily arm showed the smallest hemoglobin decline by 28 weeks ^[45]A1b. Side effects overlapped heavily with pregnancy symptoms and were reported at baseline in all groups, complicating tolerability comparisons ^[45]A1b. The takeaway: daily dosing may deliver the greatest iron load, but patient preference and adherence remain critical, no single schedule has emerged as unequivocally superior.

Emergence of Intravenous Iron

Intravenous iron was long reserved for patients who failed or could not tolerate oral therapy. The RAPIDIRON trial (secondary analysis, 2026) directly challenged that hierarchy in pregnant women with moderate iron-deficiency anemia: by 26-30 weeks, those receiving intravenous ferric carboxymaltose (FCM) or ferric derisomaltose (FDM) showed significantly greater increases in mean corpuscular volume (MCV +2.87 fL with FDM, +3.02 fL with FCM) and reticulocyte hemoglobin equivalent (Ret-He +1.32 and +1.31 pg) compared with oral ferrous sulfate ^[93]B2b. By 42 days postpartum, all hematologic parameters converged, confirming that IV iron accelerates recovery but does not alter ultimate outcomes ^[93]B2b. In neurosurgery, preoperative FCM eliminated red-cell transfusion entirely in one small randomized trial: 0% of the FCM group required transfusion versus 57.1% of controls (OR 0.03) ^[37]A1b. No adverse events were reported in that trial ^[37]A1b.

Population-Based Prevention Strategies

Efforts to prevent iron deficiency at the population level have evolved from universal iron supplements to targeted fortification. A 2021 trial in rural Bangladesh randomized 3300 infants to daily iron syrup, multiple micronutrient powders, or placebo for 3 months; no difference emerged in cognitive composite score, and the prevalence of anemia and iron deficiency actually increased in all groups by 9 months after supplementation stopped ^[29]A1b. Fortification strategies have shown more selective success. Quintuply-fortified salt (with encapsulated ferrous fumarate, zinc, vitamin B-12, folic acid, and iodine) improved vitamin B-12 and folate status in Indian preschoolers but did not significantly raise hemoglobin or ferritin ^[121]A1b. Delayed cord clamping at delivery (mean 106 s vs 9 s) has proven a simple, low-cost intervention that increases ferritin levels at 4 months without increasing hypothermia or polycythemia ^[125]A1b.

Uncovering Treatable Causes of Refractory IDA

A crucial shift in the 2000s was the recognition that a substantial fraction of unexplained, refractory iron-deficiency anemia is caused by treatable conditions rather than intrinsic iron malabsorption. Targeted screening for celiac disease, autoimmune gastritis, and Helicobacter pylori infection identifies remediable causes in 4-6%, 20-27%, and over 50% of such patients, respectively ^[11]D5. H. pylori eradication alone permanently cures iron deficiency in 64-75% of infected patients, after exclusion of other causes ^[11]D5. Autoimmune gastritis often presents as iron-deficiency anemia years before cobalamin deficiency becomes evident, a pattern missed when workup stops at endoscopy ^[11]D5. These findings moved the diagnostic workup beyond the gastrointestinal tract and established that some “refractory” IDA is actually curable with targeted antimicrobial or immunosuppressive therapy.

Modern Trends: Lower Dose Thresholds and Newer Formulations

Contemporary guidelines have shifted away from the once-routine practice of transfusing packed red blood cells for asymptomatic iron-deficiency anemia. The ASH-ASPHO Choosing Wisely campaign explicitly recommends avoiding transfusion in children with iron-deficiency anemia who are hemodynamically stable and have no active bleeding ^[109]A1c. In infants, formula with 2 mg/L iron is now considered adequate for low-risk populations, a marked departure from the earlier default of 8 mg/L, and did not increase iron deficiency or delay neurodevelopment at 12 months ^[122]A1b. Newer oral iron preparations are gaining evidence in niche populations: in children with chronic kidney disease and iron-deficiency anemia, iron polymaltose complex produced a superior hemoglobin response compared with liposomal iron, but liposomal iron caused side effects in only 3% of recipients versus 36% ^[110]A1b.

Pearl: When oral iron fails to correct anemia despite adequate adherence, do not immediately escalate to intravenous therapy; screen for H. pylori, celiac disease, and autoimmune gastritis, eradicating the underlying cause resolves IDA in two-thirds of infected patients ^[11]D5.

Building on the therapeutic arc outlined above, the complications of iron deficiency anemia (IDA), arising from the anemic state itself and from treatment, require systematic vigilance. Chronic anemia strains the cardiovascular system, and in children, neurologic development may be compromised: IDA is associated with increased morbidity including neurologic impairment, infection, heart failure, and increased mortality ^[46]D5. During pregnancy, maternal IDA raises the risk of low birth weight ^[46]D5. These downstream effects underscore why prompt correction matters.

Infection Risk and Iron Therapy

A longstanding concern is that iron supplementation might exacerbate infections, particularly in malaria-endemic regions. The TNF(-308) AA genotype, which elevates tumor necrosis factor-alpha, increases the adjusted odds of iron deficiency 8.1-fold (P = 0.001) in West African children, likely through TNF-mediated blockade of iron absorption ^[35]B3b. In such settings, careful risk-benefit assessment is mandatory ^[56]D5. Reassuringly, a recent retrospective cohort study of adults with active infections (MRSA bacteremia, pneumonia, UTI, colitis, cellulitis ) found that IV iron administration was associated with improved survival at 14 and 90 days (e.g., pneumonia: 95.7% vs 91.5% at 14 days) and greater hemoglobin recovery (e.g., +1.3 vs +1.0 g/dL for MRSA bacteremia) without evidence of exacerbated infection ^[127]B3b. However, these findings are observational and prospective confirmation is awaited.

Refractory IDA and Underlying Disorders

Unexplained or refractory IDA is itself a complication that signals an occult driver. Among patients with obscure IDA, celiac disease is present in 4-6%, autoimmune gastritis in 20-27%, and active Helicobacter pylori infection in over 50%; eradication of H. pylori permanently cures 64-75% of these cases ^[11]D5. Autoimmune gastritis with iron deficiency often precedes cobalamin deficiency by years ^{[11]D5[43]B3b}. Recognizing these entities transforms management from iron replacement alone to disease-specific therapy.

Treatment-Related Adverse Effects

Oral iron commonly causes gastrointestinal intolerance (nausea, constipation, epigastric discomfort), limiting adherence. IV iron carries a low risk of hypersensitivity reactions; modern formulations allow high-dose single infusions with an acceptable safety profile ^[56]D5. In a large infant trial in Bangladesh, daily iron syrup or multiple micronutrient powders did not increase serious adverse events or infection symptoms compared with placebo ^[29]A1b.

Progression to Other Anemias

In older patients who fail iron therapy, bone marrow examination may reveal ring sideroblasts (≥14% of erythroblasts), indicating acquired sideroblastic anemia rather than true IDA ^[25]C4. Discontinuing unnecessary iron and addressing the underlying myelodysplastic process are then critical.

Pearl: For any IDA patient who does not respond to oral iron, check for H. pylori and autoimmune gastritis before escalating to IV iron, eradicating the infection cures two-thirds of such cases ^[11]D5.

Having considered the complications of iron deficiency anemia, attention turns to its natural history and the factors that shape long-term outcomes. The untreated trajectory depends heavily on the underlying cause and the patient’s capacity to compensate. In the absence of intervention, progressively falling hemoglobin drives tissue hypoxia, cardiovascular strain, and, in severe cases, high-output heart failure and death ^[46]D5. The tempo is set by the rate of blood loss: chronic occult bleeding from a colonic malignancy can lower hemoglobin by 0.5-1 g/dL per month, while acute gastrointestinal bleeding may cause rapid decompensation over hours.

Factors shaping prognosis

The most powerful determinant is the etiologic lesion. A prospective study of 170 patients with IDA found that pan-GI endoscopy identified a potential bleeding lesion in 71.1% (95% CI 64.4-77.9), and management changed in 52.3% (95% CI 44.5-60.0) ^[4]B2b. When the source is a resectable colorectal cancer , correction of anemia after tumor removal yields a normal lifespan. In contrast, IDA from hereditary hemorrhagic telangiectasia (HHT) carries a far heavier burden: women with HHT have a 17-fold higher odds of iron infusion dependence, a threefold higher odds of red cell transfusion, and hospital admissions 14 times more frequent than women with von Willebrand disease ^[108]B2b. Epistaxis severity is the main driver; a 24‑week trial of pomalidomide in HHT reduced the Epistaxis Severity Score by a mean of -0.94 points (95% CI -1.57 to -0.31; P=0.004) ^[44]A1b.

Bariatric surgery produces a delayed but cumulative risk. In a cohort followed for a mean 31 months, the cumulative incidence of iron deficiency was 43% and of IDA 16%, with IV iron use rising 3 years post‑surgery ^[31]B3b. Malabsorptive procedures (hazard ratio 1.92, 95%) and low baseline ferritin (HR 0.96, 95% CI 0.95-0.97) predict deficiency ^[31]B3b.

Treatment outcomes

Modern IV iron formulations restore hemoglobin reliably. In a meta‑analysis of five RCTs, ferric derisomaltose compared with iron sucrose showed little difference in hemoglobin rise at 4 weeks (mean difference 0.09 g/dL, 95% CI -0.33 to 0.52; very low certainty) ^[134]A1a. In pregnancy, IV ferumoxytol produced a median hemoglobin increase of 1.10 g/dL at 4 weeks vs. 0.40 g/dL with oral ferrous sulfate (P<0.001), and anemia resolved in 92.5% vs. 65.0% ^[135]A1b. Single‑dose ferric derisomaltose in the second or third trimester yielded a mean rise of 1.3 g/dL from baseline to delivery, with improved fatigue scores and neonatal iron stores ^[50]C4. Preoperative administration is equally effective: in patients facing neurosurgical clipping for unruptured aneurysms, IV ferric carboxymaltose eliminated perioperative transfusions (0% vs. 57.1% in controls; OR 0.03, 95%) ^[37]A1b.

Long‑term risks

Even corrected anemia carries residual hazard. A systematic review found that lower hemoglobin predicts higher short‑term mortality in acute pulmonary embolism (HR 1.16 per 1 g/dL decrease) and increased symptomatic VTE in hospitalized patients (RR 1.94) ^[136]B2a. Iron‑deficiency anemia itself raised the odds of VTE in population‑based data (OR 1.43) ^[136]B2a. However, IV iron during acute infection does not worsen outcomes: a large propensity‑matched study showed higher survival at 14 and 90 days when IV iron was given during MRSA bacteremia, pneumonia, UTI, colitis, or cellulitis , with hemoglobin recovery 0.3-0.8 g/dL greater than controls ^[127]B3b.

Prognosis in children

Pediatric IDA, if untreated, is associated with neurologic developmental impairment, increased infection risk, and heart failure ^[46]D5. In rural Bangladesh, 3‑month supplementation with iron syrup or multiple micronutrient powders did not improve cognitive scores but did reduce the prevalence of anemia and iron deficiency at 9‑month follow‑up, with no excess of serious adverse events ^[29]A1b. Long‑term prognosis is excellent once iron stores are repleted, provided the underlying cause (e.g., dietary inadequacy, hookworm) is addressed.

Pearl: The prognosis of iron deficiency anemia is excellent when the underlying cause is identified and treated; mortality is driven by the causative lesion, not the anemia itself.

The excellent prognosis of IDA with appropriate treatment hinges on its recognition and correction in populations where iron demands are highest and consequences most severe. Management must be tailored to the unique physiology and vulnerabilities of each group.

Pregnancy

Oral iron remains first-line. A pilot trial comparing 200 mg ferrous sulfate daily, alternate days, or three times per week found the lowest adherence in the daily arm (47% vs 62% and 61%), but daily dosing best preserved hemoglobin through 28 weeks 45 . Alternate-day regimens improve tolerance when side effects limit adherence. For moderate-severe IDA after the first trimester, intravenous iron achieves faster correction. In a randomized trial, IV ferumoxytol (510-1020 mg depending on hemoglobin) raised hemoglobin at 4 weeks by a median 1.10 g/dL versus 0.40 g/dL with oral ferrous sulfate, and resolved anemia in 92.5% vs 65.0% of women 135 . Similarly, IV ferric carboxymaltose and ferric derisomaltose improved MCV, reticulocyte hemoglobin equivalent (Ret‑He), and other indices more rapidly than oral therapy 93 . However, large pragmatic trials from low‑resource settings showed that biochemical superiority did not consistently translate into better maternal or neonatal outcomes 96 ; shared decision-making is essential. Early pregnancy is a contraindication to iron infusions 8 ; use after 12 weeks. Breastfeeding : maternal iron supplementation is safe and supports repletion. Calcium supplementation (500 vs 1500 mg daily) does not affect iron status 89 . Mobile‑health nutritional interventions improved hemoglobin in 9 of 11 trials 139 and may enhance adherence.

Pediatrics

Nearly half of preschool‑age children worldwide are anemic, mostly from IDA 46 . Diagnosis requires age‑specific thresholds, and asymptomatic children with IDA and no active bleeding should not receive red blood cell transfusion 109 . If conventional oral iron causes gastrointestinal intolerance, liposomal iron offers an alternative: at 6 months, it produced a greater hemoglobin increase (mean difference 0.96 g/dL) and fewer adverse events (RR 0.29) compared with conventional iron 87 . In children who fail to respond to oral iron, suspect iron refractory iron deficiency anemia (IRIDA) caused by TMPRSS6 mutations: anemia appears in the postnatal period, hepcidin is inappropriately high, and only slow response to intravenous iron occurs 91 . Early recognition avoids unnecessary diagnostic delays.

Elderly

Iron deficiency anemia in older adults should prompt evaluation for autoimmune gastritis . Patients presenting with IDA are on average 21 years younger than those with macrocytic anemia from the same autoimmune process, suggesting a decades‑long progression from iron deficiency to cobalamin depletion 138 . Concurrent thyroid disease (20%) and diabetes (8%) are common 138 . Check parietal cell antibodies , gastrin, and B₁₂ levels; dual deficiency (iron + B₁₂) may require combined replacement. Treatment thresholds may be lower because comorbidities amplify the effects of anemia.

Immunocompromised and Renal/Hepatic Impairment

Intravenous iron carries a small risk of acute hypersensitivity reactions, particularly in patients with multiple drug allergies, severe atopy, or systemic inflammatory conditions 8 . In immunocompromised hosts, weigh the risk of infection and iron overload against the benefits of rapid repletion. In chronic kidney disease, intravenous iron combined with erythropoiesis‑stimulating agents is standard; dosing should follow nephrology guidelines. Hepatic impairment does not contraindicate iron therapy, but underlying iron overload disorders (e.g., hemochromatosis ) should be excluded before initiating supplementation.

Pearl: In pregnant women with IDA, IV iron corrects anemia faster than oral iron, resolving anemia in 92.5% vs 65% 135 , but large pragmatic trials did not find consistent improvement in maternal/neonatal outcomes, making shared decision-making critical; in asymptomatic children with IDA, avoid RBC transfusion 109 .

Building on the importance of iron repletion in pregnancy and other vulnerable groups, prevention and early detection of iron deficiency anemia (IDA) require a structured approach that targets populations at risk and identifies remediable underlying causes.

Primary Prevention

For pregnant women, universal daily supplementation with 60 mg of elemental iron (as iron and folic acid) is standard in many settings ^[89]B2b. Low-dose (500 mg) and high-dose (1500 mg) calcium supplements given several hours apart from iron do not differ in their effect on third-trimester hemoglobin or iron deficiency anemia ^[89]B2b. Mobile health (mHealth) interventions, particularly those using WhatsApp Messenger, have shown large effect sizes (>0.8) on hemoglobin improvement, with within- and between-group differences exceeding 1 g/dL in some studies ^[139]A1a. The SOGC guideline (2026) emphasizes that prevention, early identification, and treatment of IDA is a cost-effective strategy that reduces the need for blood transfusion ^[66]A1c.

Screening Recommendations

Pregnant women: The Philippine Clinical Practice Guidelines (2025) recommend screening for IDA as part of routine prenatal care ^[130]D5. The SOGC guideline similarly advocates for universal screening in pregnancy, with hemoglobin and ferritin assessment at the first prenatal visit and again in the third trimester ^[66]A1c.

Non-pregnant women of reproductive age: The SOGC guideline suggests targeted screening for women with heavy menstrual bleeding, a history of IDA, or dietary risk factors ^[66]A1c. Screening should include a complete blood count and serum ferritin; a ferritin <30 ng/mL confirms iron deficiency even if hemoglobin is normal.

Older adults and patients with gastrointestinal symptoms: Iron deficiency anemia is a strong predictor of early-onset colorectal cancer (EOCRC). In a nested case-control study, IDA carried an odds ratio of 3.56 for EOCRC, independent of other risk factors ^[67]B3b. Another study confirmed IDA as a significant predictor across all models ^[51]B3b. Therefore, new-onset IDA in men or postmenopausal women (and increasingly in adults <50 years) should trigger prompt colonoscopy to exclude colorectal neoplasia. The presence of IDA may also justify screening colonoscopy before age 45 in symptomatic or high-risk individuals ^[67]B3b.

Infants and toddlers: Routine screening for IDA is recommended at 9-12 months of age in high-prevalence populations, with repeat testing at 12-24 months if risk factors persist.

Secondary Prevention (Preventing Recurrence)

In patients with unexplained or refractory IDA, screening for celiac disease, autoimmune gastritis, and Helicobacter pylori infection is recommended ^[11]D5. About 4%-6% of such patients have celiac disease, 20%-27% have autoimmune gastritis, and >50% have active H. pylori infection; eradication of H. pylori permanently cures IDA in 64%-75% of cases ^[11]D5. Identifying and treating these underlying conditions prevents recurrence and should be pursued after negative endoscopic evaluation.

Vaccine-Related Considerations

No specific vaccine contraindications exist for patients with IDA. Routine immunizations should proceed as scheduled. Severe iron deficiency may impair lymphocyte proliferation and humoral immune responses, so correcting deficiency before elective vaccination is reasonable, though not mandatory. Iron therapy does not interfere with vaccine safety or efficacy.

Patient Education Points

Patients should be counseled to: take oral iron on an empty stomach or with vitamin C to enhance absorption; separate iron and calcium supplements by at least 2 hours; continue supplementation for 3 months after hemoglobin normalization to replenish stores; and report any recurrence of fatigue, pallor, or pica to prompt reevaluation for ongoing blood loss or malabsorption.

Pearl: New-onset IDA in adults over 40 years (or younger with alarm symptoms) is a red flag for colorectal cancer, order colonoscopy even when hemoglobin is only mildly low, as the odds ratio for early-onset disease is 3.56 ^[67]B3b.