A 60-year-old man being evaluated for weight loss is found to have persistently elevated serum alkaline phosphatase. Isoenzyme analysis identifies a band that migrates in the position of placental alkaline phosphatase despite the absence of pregnancy, and this band is resistant to both heat and L-phenylalanine inhibition. This finding is classically associated with:

• A Paget disease of bone
• B Familial hypophosphatasia
• C Extrahepatic biliary obstruction
• D Malignancy, especially bronchogenic carcinoma ✓

Explanation

The Regan isoenzyme is a carcinoplacental alkaline phosphatase expressed by certain tumours, classically bronchogenic carcinoma and other malignancies. It is biochemically identical to placental ALP, so it shows marked heat stability and resistance to L-phenylalanine inhibition. Paget disease produces a bone-type, heat-labile isoenzyme, and obstructive jaundice produces a liver-type band accompanied by raised GGT, so both are excluded by the isoenzyme profile described.

Reference: Tietz Textbook of Clinical Chemistry and Molecular Diagnostics, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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