In acute intermittent porphyria, urine turns port-wine red on standing. What causes this colour change?

• A Conversion of ALA to uroporphyrin by light
• B Haemoglobin breakdown from haemolysis
• C Myoglobinuria from rhabdomyolysis
• D Oxidation of PBG to porphobilin in alkaline urine ✓

Explanation

PBG in urine oxidises spontaneously to porphobilin, a dark red pigment, especially on exposure to light and air. This is a classic bedside observation. Haemolysis does not occur in AIP. Myoglobinuria is not a feature. ALA does not convert to uroporphyrin non-enzymatically in urine.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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