An immunoprecipitation assay for high molecular weight alkaline phosphatase in human serum

The serum of patients with obstructive liver disease may contain a high molecular weight form of alkaline phosphatase (high Mr alkaline phosphatase). The presence of this form of alkaline phosphatase is associated with hepatic malignancies. We have investigated the use of anti-alkaline phosphatase monoclonal antibodies which do not bind high Mr alkaline phosphatase in assays for high Mr alkaline phosphatase. Direct immunoprecipitation of liver and bone alkaline phosphatase with solid phase anti-liver alkaline phosphatase antibody (which also reacts with bone alkaline phosphatase) and measurement of the residual supernatant alkaline phosphatase activity led to a precise assay. Intestinal alkaline phosphatase interfered in this assay which, consequently, was of little use in the differential diagnosis of liver disease. Indirect precipitation of liver, bone, placental and intestinal alkaline phosphatase by soluble anti-liver alkaline phosphatase (which reacts with liver and bone alkaline phosphatases), soluble anti-intestinal alkaline phosphatase (which reacts with placental and intestinal alkaline phosphatases) and solid phase anti-mouse IgG led to an assay which, although less precise, showed more promise of being useful clinically.