Alkaline phosphatase (ALP) isoenzymes can distinguish the source of elevation. The heat-stable ALP isoenzyme (resistant to heating at 56°C for 15 minutes) originates from:
- A Liver
- B Placenta ✓
- C Bone
- D Intestine
Correct answer: B. Placenta
Explanation
Among ALP isoenzymes, the placental isoenzyme (Regan isoenzyme) is uniquely heat-stable: it retains >50% activity after heating at 56°C for 15 minutes, or even 65°C in some protocols. This heat stability is exploited in the heat fractionation test. Bone ALP is heat-labile. Liver ALP shows intermediate heat stability. Intestinal ALP is also relatively heat-labile. Elevated heat-stable ALP in a non-pregnant adult may indicate hepatocellular carcinoma or other malignancies expressing the Regan isoenzyme as a tumour marker.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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