Positive placental staining for alkaline phosphatase corresponding with extreme elevation of serum alkaline phosphatase during pregnancy.

Placental ALP (ALP(h)) is a membrane-anchored, heat-stable enzyme produced by the syncytiotrophoblast. We report a case of a patient presenting in the third trimester with extreme increased levels of ALP(h). A 40-year-old woman, gravida 2, para 1, was admitted to the high risk pregnancy unit at 30 weeks of gestation for evaluation of an incidental finding of marked isolated elevation in serum ALP(h).