How to manage microcytic anemia?

Management of Microcytic Anemia

Start oral ferrous sulfate 200 mg three times daily immediately, but first obtain serum ferritin, transferrin saturation, and RDW to confirm iron deficiency and rule out other causes of microcytic anemia. 1

Immediate Diagnostic Workup

Before initiating treatment, obtain these specific tests to differentiate the cause:

• Serum ferritin is the single most specific test for iron deficiency: <15 μg/L indicates absent iron stores, <30 μg/L indicates low stores, and a cut-off of 45 μg/L provides optimal sensitivity and specificity. 1, 2
• Check transferrin saturation (TSAT), which is more sensitive than hemoglobin alone for detecting iron deficiency. 1
• Evaluate RDW to distinguish iron deficiency from thalassemia: Low MCV with RDW >14.0% strongly suggests iron deficiency anemia, while low MCV with RDW ≤14.0% suggests thalassemia minor. 1, 2, 3

First-Line Treatment for Iron Deficiency Anemia

Once iron deficiency is confirmed:

• Prescribe ferrous sulfate 200 mg (providing 65 mg elemental iron) three times daily for at least three months after hemoglobin normalizes to replenish iron stores. 1, 2, 3
• Add ascorbic acid (vitamin C) to enhance iron absorption if tolerated. 1, 2
• If ferrous sulfate causes intolerable gastrointestinal side effects, switch to ferrous gluconate or ferrous fumarate. 1

Expected Response and Monitoring Timeline

• A good response is defined as hemoglobin rise ≥10 g/L (≥1 g/dL) within 2 weeks, which confirms iron deficiency. 1, 3
• Expect hemoglobin increase of at least 2 g/dL within 4 weeks of starting treatment. 1, 3
• Monitor hemoglobin and MCV at 2 weeks, 4 weeks, 3 months, then every 3 months for the first year, then annually. 3

When Oral Iron Fails: Red Flags for Alternative Diagnoses

If hemoglobin does not rise appropriately within 2-4 weeks, immediately investigate for:

• Genetic disorders of iron metabolism (particularly Iron-Refractory Iron Deficiency Anemia/IRIDA due to TMPRSS6 defects): Look for low TSAT combined with low-normal ferritin (>20 mg/L), family history of refractory anemia, or anemia incompletely responsive to oral iron. 1, 3
• X-linked Sideroblastic Anemia (ALAS2 defects): Trial pyridoxine (vitamin B6) 50-200 mg daily initially, with lifelong maintenance at 10-100 mg daily if responsive. 1, 3
• Thalassemia minor: Suggested by normal or near-normal RDW with low MCV. 1
• Anemia of chronic disease: Check ESR, CRP, and evaluate for underlying inflammatory conditions. 4

Intravenous Iron Indications

• Consider IV iron if malabsorption is present (celiac disease, inflammatory bowel disease, post-gastric bypass), with expected hemoglobin increase of at least 2 g/dL within 4 weeks. 1, 3
• IRIDA requires repeated intravenous iron (iron sucrose or ferric gluconate) as oral iron is ineffective and delays appropriate treatment. 1, 3
• Monitor serum ferritin levels to avoid iron overload toxicity—do not exceed 500 μg/L, especially in children and adolescents. 1, 2

Critical Pitfalls to Avoid

• Do not assume all microcytic anemia is iron deficiency: Failure to check ferritin and RDW leads to unnecessary iron therapy in thalassemia or anemia of chronic disease. 1, 3
• Do not overlook combined deficiencies: Iron deficiency can coexist with B12 or folate deficiency—check these if response to iron is suboptimal. 2, 3
• Do not use oral iron for IRIDA: This genetic disorder is iron-refractory by definition and requires IV iron. 3
• In genetic sideroblastic anemias, iron overload causes more morbidity and mortality than the anemia itself—unrecognized tissue iron loading can cause severe organ damage. 3
• Investigate the underlying cause of iron deficiency: In adults, this mandates evaluation for gastrointestinal blood loss (melena, hematochezia, occult bleeding) or malabsorption (celiac disease). 1