A 28-year-old woman with iron deficiency anemia (Hb 7.8 g/dL) is started on oral ferrous sulfate 200 mg three times daily. She asks when improvement will be seen. Which laboratory finding appears first during a response to oral iron therapy?

• A Normalization of serum ferritin
• B Rise in hemoglobin by 1 g/dL within 48 hours
• C Correction of mean corpuscular volume to normal within 1 week
• D Peak reticulocyte count 7 to 10 days after starting treatment ✓

Explanation

The earliest measurable response is a reticulocyte peak at 7 to 10 days, reflecting marrow output before hemoglobin rises. Hemoglobin then increases slowly, roughly 1 to 2 g/dL over 3 weeks, and full correction takes up to 2 months followed by 3 months of continued therapy to replenish stores. Ferritin is the last parameter to normalize, so option A is the tempting distractor that fails.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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