A patient with suspected folate deficiency undergoes a histidine load test. Increased urinary excretion of which metabolite supports the diagnosis?

• A Xanthurenic acid
• B Homogentisic acid
• C Methylmalonic acid
• D Formiminoglutamic acid (FIGLU) ✓

Explanation

Histidine catabolism proceeds through formiminoglutamate, which requires tetrahydrofolate to accept the formimino group before yielding glutamate. In folate deficiency, FIGLU accumulates and spills into urine after a histidine load, forming the basis of the FIGLU excretion test. Methylmalonic acid indicates vitamin B12 deficiency, xanthurenic acid reflects vitamin B6 status via tryptophan metabolism, and homogentisic acid marks alkaptonuria.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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