A sensitive immunochemical method for the determination of the Regan isoenzyme in serum.

An enzymatic, immunochemical test system has been developed which allows quantitation of minute amounts of the Regan isoenzyme of alkaline phosphatase. The basis of the method is the concentration (tenfold) of the Regan isoenzyme by reaction with a monospecific antiserum to placenta! alkaline phosphatase, insolubilized by polymerization with ethyl chloroformate. This concentration is achieved by incubating heat-inactivated serum with the antibody and by subsequent centrifugation. The pellet containing the active enzyme-antibody complex is immediately assayed for enzyme activity. We studied sera from 91 normal healthy adults and 112 cancer patients to determine the presence of the Regan isoenzyme. Detectable Regan isoenzyme activity was found in 89 of 91 normal healthy adults. Three of the normal sera contained a level of the isoenzyme that fell above 2 S.D. from the mean. In the case of patients with neoplastic disease, 106 of 112 sera had detectable Regan isoenzyme activity and only 11 sera showed elevated activities. Cancer sera with abnormal Regan levels contained 3 to 300 times the average normal value.