What is the appropriate management for a patient with microcytic anemia, as indicated by low MCH and normal hematocrit?

Management of Low MCH with Normal Hematocrit

Start oral iron supplementation with ferrous sulfate 200 mg three times daily and investigate the underlying cause of iron deficiency, as this presentation indicates microcytic anemia despite the normal hematocrit. 1

Understanding the Clinical Picture

• Low MCH (mean corpuscular hemoglobin) indicates microcytic hypochromic red blood cells, which is characteristic of iron deficiency even when hematocrit appears normal. 1
• MCH is more reliable than MCV as a marker of iron deficiency because it's less dependent on storage conditions and is reduced in both absolute and functional iron deficiency. 1
• A normal hematocrit does not exclude iron deficiency—early iron deficiency or mild anemia can present with low MCH before hematocrit drops significantly. 2

Diagnostic Confirmation

Measure serum ferritin immediately as the single most useful test for confirming iron deficiency:

• Ferritin <15 μg/L indicates absent iron stores. 1
• Ferritin <30 μg/L indicates low body iron stores. 1
• A cut-off of 45 μg/L provides optimal sensitivity and specificity for iron deficiency in practice. 1
• If ferritin is between 30-100 μg/L and inflammation is suspected, add transferrin saturation (TSAT)—a TSAT <16-20% confirms iron deficiency. 1

Check RDW (red cell distribution width) to differentiate causes:

• Low MCV with RDW >14.0% suggests iron deficiency anemia. 1
• Low MCV with RDW ≤14.0% suggests thalassemia minor. 1

First-Line Treatment

Begin oral iron supplementation immediately while investigating the underlying cause:

• Ferrous sulfate 200 mg three times daily for at least three months after correction of anemia to replenish iron stores. 1
• Alternative formulations include ferrous gluconate or ferrous fumarate if ferrous sulfate is not tolerated. 1
• Adding ascorbic acid enhances iron absorption. 1

Monitor response to confirm diagnosis:

• Hemoglobin should rise ≥10 g/L within 2 weeks if iron deficiency is the cause. 1
• A good response to iron therapy (hemoglobin rise ≥10 g/L within 2 weeks) confirms iron deficiency. 1

Investigate the Underlying Cause

All adults with confirmed iron deficiency require investigation for the source of iron loss:

• In men and post-menopausal women, gastrointestinal blood loss is the most common cause—consider upper endoscopy with small bowel biopsy and colonoscopy to exclude malignancy. 3
• In pre-menopausal women, assess menstrual blood loss history first, but do not assume this is the cause without evaluation. 1
• Screen for celiac disease with tissue transglutaminase antibodies, as malabsorption is a common cause. 1
• Evaluate for NSAID use, which commonly causes occult GI bleeding. 3
• Consider dietary inadequacy, particularly in vegetarians or those with restricted diets. 3

Management of Treatment Failure

If no response to oral iron within 2-4 weeks, consider:

• Non-compliance or inadequate dosing. 1
• Ongoing blood loss exceeding replacement capacity. 1
• Malabsorption disorders (celiac disease, H. pylori infection, autoimmune atrophic gastritis, previous gastric surgery). 1
• Switch to intravenous iron (iron sucrose or iron gluconate) if malabsorption is confirmed—expect hemoglobin increase of at least 2 g/dL within 4 weeks. 1

Consider rare genetic disorders if refractory to both oral and IV iron:

• IRIDA (iron-refractory iron deficiency anemia) presents with remarkably low TSAT, low-to-normal ferritin, and failure to respond to oral iron. 1
• Genetic testing for SLC11A2, STEAP3, SLC25A38, ALAS2, or ABCB7 defects if extreme microcytosis (MCV <70) or family history of refractory anemia. 1

Critical Pitfalls to Avoid

• Do not assume thalassemia without testing: Order hemoglobin electrophoresis only if microcytosis persists with normal iron studies, appropriate ethnic background, or MCV disproportionately low relative to degree of anemia. 1
• Do not overlook combined deficiencies: Check vitamin B12 and folate if RDW is elevated, as combined deficiencies can mask typical microcytic picture. 1
• Do not stop investigating after starting iron: Even with treatment response, the underlying cause must be identified to prevent recurrence. 3
• Do not assume normal ferritin excludes iron deficiency in inflammatory states: Ferritin can be falsely elevated by inflammation, malignancy, or hepatic disease—levels up to 100 μg/L may still represent iron deficiency with concurrent inflammation. 3, 1

Long-Term Monitoring

• Monitor hemoglobin concentration and red cell indices at three-monthly intervals for one year, then after a further year. 1
• Provide additional oral iron if hemoglobin or MCV falls below normal. 1
• Continue iron supplementation for at least three months after anemia correction to fully replenish iron stores. 1