Which laboratory finding is most specific for riboflavin (vitamin B2) deficiency?
- A Elevated erythrocyte glutathione reductase activation coefficient ✓
- B Elevated serum methylmalonic acid
- C Increased urinary xanthurenic acid after tryptophan load
- D Elevated plasma pyruvate after glucose load
Correct answer: A. Elevated erythrocyte glutathione reductase activation coefficient
Explanation
Glutathione reductase is an FAD-dependent enzyme; the activation coefficient measures how much enzyme activity increases when FAD is added in vitro, and a high value indicates tissue riboflavin depletion. Xanthurenic acid elevation (option C) reflects pyridoxine deficiency via kynureninase impairment, and post-glucose pyruvate rise (option D) points to thiamine deficiency through pyruvate dehydrogenase failure.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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