Solid-phase direct immunoassay for serum intestinal and placental alkaline phosphatase

Antibodies against placental alkaline phosphatase (PAP) share antigenic determinants with the intestinal isoenzyme (IAP) and vice versa. Both isoenzymes can be found as part of the total activity of alkaline phosphatase (AP) in the serum. Using antibody-coated polystyrene tubes, a simple and sensitive immunoassay was developed which allows the quantitative determination of IAP or PAP without interference of the cross-reacting isoenzyme. The presence and amount of IAP depends on the ABO blood group, secretory status and the oral fat intake. The serum IAP in healthy fasted individuals was found up to 8 U/I in secretors of blood group O and B and below 1 U/I in non-secretors and blood group A donors. In screening tests of various pathological sera. IAP was found elevated up to 100 U/I in idiopathic hyper-AP-aemia and some liver cirrhosis patients.