How should a patient with microcytic anemia (hemoglobin 118 g/L, low MCH) be managed?

Management of Microcytic Anemia (Hemoglobin 118 g/L with Low MCH)

Start oral ferrous sulfate 200 mg three times daily immediately and investigate the underlying cause of iron loss, as this presentation most likely represents iron deficiency anemia requiring both treatment and diagnostic workup. 1, 2

Immediate Diagnostic Steps

Measure serum ferritin first - this is the single most powerful test for confirming iron deficiency. 2

• Ferritin <15 μg/L confirms absent iron stores 2
• Ferritin <30 μg/L indicates low body iron stores 1
• Ferritin <45 μg/L provides optimal sensitivity and specificity in clinical practice 1, 2
• If ferritin is normal or elevated, add transferrin saturation to detect functional iron deficiency 1

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

• Low MCV with RDW >14.0% strongly suggests iron deficiency anemia 1, 2
• Low MCV with RDW ≤14.0% suggests thalassemia minor 1

MCH is more reliable than MCV as a marker because it's less dependent on storage conditions and is reduced in both absolute and functional iron deficiency. 1

First-Line Treatment

Prescribe oral ferrous sulfate 200 mg (containing 65 mg elemental iron) three times daily. 1, 2, 3

• Continue for at least 3 months after hemoglobin normalizes to replenish iron stores 1, 2
• Alternative formulations (ferrous gluconate or ferrous fumarate) can be used if ferrous sulfate is not tolerated 1
• Adding ascorbic acid enhances iron absorption 1

Expected response within 2 weeks:

• Hemoglobin should rise ≥10 g/L (≥1 g/dL) if iron deficiency is the cause 1, 2
• This response confirms the diagnosis of iron deficiency anemia 1, 2

Mandatory Investigation for Underlying Cause

Do not simply treat the anemia - you must identify the source of iron loss. 1, 2

For adults with confirmed iron deficiency:

• Men with Hb <110 g/L warrant fast-track GI referral 1
• Non-menstruating women with Hb <100 g/L warrant fast-track GI referral 1
• Investigation should be considered at any level of anemia with confirmed iron deficiency 1

Most common causes to evaluate:

• Gastrointestinal blood loss (melena, hematochezia, occult bleeding) - most common in men and post-menopausal women 1, 2
• Menstrual blood loss - most common in premenopausal women 1
• Malabsorption disorders (consider celiac disease screening if suspected) 1
• Dietary inadequacy 1

If Patient Fails to Respond to Oral Iron

Consider these possibilities if hemoglobin does not rise ≥10 g/L within 2 weeks: 1, 2

• Non-compliance with medication 1
• Ongoing blood loss exceeding replacement 1
• Malabsorption (consider IV iron) 1
• Rare genetic disorders of iron metabolism (IRIDA, SLC11A2, TMPRSS6 defects) 1

For malabsorption or severe cases:

• Intravenous iron (iron sucrose or iron gluconate) should be considered 1
• Expected hemoglobin increase of at least 2 g/dL within 4 weeks 1

Alternative Diagnoses to Consider

Order hemoglobin electrophoresis if: 1

• Microcytosis with normal iron studies 1
• MCV disproportionately low relative to degree of anemia 1
• Appropriate ethnic background for thalassemia 1
• Extreme microcytosis (MCV <70) or family history present 1

Other causes of microcytic anemia to differentiate:

• Anemia of chronic disease (ferritin normal/elevated, low transferrin saturation) 1
• Thalassemia (normal RDW, normal/elevated ferritin) 1
• Sideroblastic anemia (may respond to pyridoxine 50-200 mg daily for ALAS2 defects) 4, 1

Monitoring Protocol

Follow-up schedule: 1, 2

• Monitor hemoglobin and red cell indices at 3-month intervals for one year 1, 2
• Recheck again at 2 years 2
• Provide additional oral iron if hemoglobin or MCV falls below normal 1, 2

Monitor for iron overload if:

• Patient receives multiple transfusions 1
• Long-term iron therapy is required 1
• Consider MRI of liver to detect toxic iron loading early in specific cases 1

Critical Pitfalls to Avoid

• Do not assume all microcytic anemia is iron deficiency - anemia of chronic disease, thalassemia, and sideroblastic anemia must be differentiated to avoid unnecessary iron therapy 1
• Do not overlook combined deficiencies - iron deficiency can coexist with B12 or folate deficiency 1
• Do not stop iron therapy when hemoglobin normalizes - continue for 3 months after correction to replenish stores 1, 2
• Do not fail to investigate the source of iron loss - treating without finding the cause risks missing serious pathology like GI malignancy 1, 2