A 35-year-old woman with confirmed iron deficiency anemia (serum ferritin 5 ng/mL) is started on oral ferrous sulfate 200 mg three times daily. What is the earliest expected hematological response to therapy?

• A Hemoglobin rises by 1 g/dL within 24 hours
• B MCV returns to normal within 1 week
• C Serum ferritin normalizes within 48 hours
• D Reticulocyte count peaks between days 5 and 7 ✓

Explanation

After initiating iron therapy, reticulocytosis begins within 2-3 days and peaks at 5-7 days, reflecting new red cell production. Hemoglobin rises gradually over 2-4 weeks. MCV normalization takes 6-8 weeks as microcytic cells are replaced. Ferritin replenishes last and may take months to normalize after hemoglobin recovery.

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

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