A 55-year-old woman presents with fatigue and pallor. CBC shows Hb 8.2 g/dL, MCV 68 fL, MCH 20 pg, RDW 18%. Serum ferritin is 6 ng/mL, serum iron 38 μg/dL, TIBC 480 μg/dL (elevated). Peripheral smear shows hypochromic microcytic cells with pencil cells. Which is the single most important next step before initiating iron therapy?

• A Start IV iron infusion immediately
• B Identify and treat the underlying cause of iron deficiency ✓
• C Order a bone marrow biopsy to confirm iron-deficient erythropoiesis
• D Begin oral ferrous sulfate without further investigation

Explanation

Iron deficiency anemia in an adult should never be simply treated without identifying the underlying etiology. In premenopausal women, the most common cause is menstrual blood loss; in post-menopausal women or men, gastrointestinal blood loss from colorectal malignancy or peptic ulcer must be excluded urgently. Treating iron deficiency without identifying the source may delay diagnosis of an underlying cancer. The TIBC > 400 and low ferritin confirm iron deficiency, but the priority is establishing the cause.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.