What is the treatment approach for a patient with microcytic (low MCV) hypochromic (low MCH) anemia?

Management of Low MCV and MCH (Microcytic Hypochromic Anemia)

Start oral ferrous sulfate 200 mg (65 mg elemental iron) three times daily immediately, as iron deficiency is the most common cause and a good response to therapy (hemoglobin rise ≥10 g/L within 2 weeks) confirms the diagnosis even if iron studies are equivocal. 1, 2

Diagnostic Confirmation

Before or concurrent with treatment initiation, confirm iron deficiency with iron studies:

• Serum ferritin is the single most useful marker for iron deficiency anemia 1

  • Ferritin <15 μg/L indicates absent iron stores (99% specificity) 1
  • Ferritin <30 μg/L indicates low body iron stores 1
  • Use a cut-off of 45 μg/L for optimal sensitivity and specificity in practice 1, 2
  • Ferritin >150 μg/L makes absolute iron deficiency unlikely, even with inflammation 1

• Add transferrin saturation if ferritin is falsely normal due to inflammation (ferritin is an acute phase protein) 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

Treatment Protocol

First-Line Oral Iron Therapy

• Ferrous sulfate 200 mg (65 mg elemental iron) three times daily 2, 3, 4
• Continue for at least 3 months after anemia correction to replenish iron stores 2, 3
• Add ascorbic acid (vitamin C) to enhance absorption 2, 3
• Alternative formulations if not tolerated: ferrous gluconate or ferrous fumarate 2
• Do not crush or chew tablets 4

Expected Response and Monitoring

• Hemoglobin should rise ≥10 g/L within 2 weeks if iron deficiency is the cause 1, 2
• Monitor hemoglobin and red cell indices at 3-month intervals for one year, then again after another year 2, 3
• Provide additional oral iron if hemoglobin or MCV falls below normal 2, 3

When Oral Iron Fails

If no response within 2-4 weeks, consider:

Intravenous Iron Indications

• Malabsorption (celiac disease, inflammatory bowel disease, gastric bypass) 2, 3
• Expected hemoglobin increase of at least 2 g/dL within 4 weeks of IV iron 2, 3
• Options include iron dextran, iron gluconate, or iron sucrose 5

Alternative Diagnoses to Exclude

Check RDW (red cell distribution width) to differentiate causes: 2, 3

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

Order hemoglobin electrophoresis if: 1

• Microcytosis with normal iron studies
• Appropriate ethnic background (Mediterranean, Asian, African descent)
• MCV disproportionately low relative to degree of anemia (suggests thalassemia)

Consider genetic disorders of iron metabolism or heme synthesis if: 2, 3

• Refractory to oral iron with confirmed compliance
• Family history of refractory anemia
• Ferritin low-normal (>20 mg/L) with low transferrin saturation

Special Genetic Causes Requiring Different Treatment

• X-linked sideroblastic anemia (ALAS2 defects): Start pyridoxine (vitamin B6) 50-200 mg daily initially, then maintain lifelong at 10-100 mg daily 2
• IRIDA (TMPRSS6 defects): Usually resistant to oral iron; requires repeated IV iron 2
• Severe genetic disorders: May require erythropoietin, transfusions, or stem cell transplantation 2

Critical Pitfalls to Avoid

• Don't assume all microcytic anemia is iron deficiency: Anemia of chronic disease, thalassemia, and sideroblastic anemia require differentiation to avoid unnecessary iron therapy 2
• Don't overlook combined deficiencies: Iron deficiency can coexist with B12 or folate deficiency 2, 3
• Don't miss the 7% of patients with both thalassemia trait and iron deficiency: Check ferritin even when thalassemia is diagnosed 3
• Always investigate the source of iron loss in adults: Gastrointestinal blood loss from ulcer or malignancy must be excluded 1, 6, 7
  • Men with Hb <110 g/L or non-menstruating women with Hb <100 g/L warrant fast-track GI referral 1
  • Consider investigation at any level of anemia with confirmed iron deficiency, especially with more severe degrees 1