A healthy 32-year-old woman in her third trimester of pregnancy has routine labs showing alkaline phosphatase of 280 U/L (normal 120 U/L) with normal bilirubin, AST, ALT and GGT. She is asymptomatic. The MOST appropriate interpretation is:

• A Intrahepatic cholestasis of pregnancy requiring urgent delivery planning
• B Physiologic elevation from the placental isoenzyme of alkaline phosphatase ✓
• C Occult vitamin D deficiency with secondary hyperparathyroidism
• D Early primary biliary cholangitis unmasked by pregnancy

Explanation

The placenta produces a heat-stable alkaline phosphatase isoenzyme, and maternal serum ALP rises progressively in the third trimester, often reaching two to three times the upper limit, returning to normal within weeks after delivery. Normal GGT, bile acids implied by the clinical picture, and absence of pruritus argue against intrahepatic cholestasis of pregnancy, which is the key distractor to exclude before labeling the result pathologic.

Reference: Harper's Illustrated Biochemistry, 31st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.