Histidine is degraded to glutamate via formiminoglutamate (FIGLU). In severe folate deficiency, which laboratory finding follows from this pathway?
- A Decreased urinary FIGLU after histidine loading
- B Increased urinary FIGLU excretion, the basis of the FIGLU test ✓
- C Elevated serum methylmalonic acid with normal homocysteine
- D Increased urinary orotic acid from impaired pyrimidine recycling
Correct answer: B. Increased urinary FIGLU excretion, the basis of the FIGLU test
Explanation
Formiminoglutamate transfers its formimino group to tetrahydrofolate during histidine catabolism. Without THF, FIGLU accumulates and spills into urine, so a histidine load produces excess urinary FIGLU, the classical FIGLU test for folate deficiency. Option C describes vitamin B12 deficiency, where methylmalonic acid rises but homocysteine also rises, so it does not match. Orotic acid reflects urea cycle or pyrimidine pathway blocks, unrelated to folate.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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