Relative merits of the biliary alkaline phosphatase isoenzyme and lipoprotein-X in diagnosis of cholestasis.

There are many reports on the appearance of a typical isoenzyme of alkaline phosphatase (EC 3.1.3.1; API)2 in serum of patients suffering from biliary obstruction. According to the characteristics observed in various studies, this API has variouslybeen termed “high molecular weight” (1), “origin,” “stationary,” “particulate” (2), “bile,” “cholestatic,” “pathological biliary” (3, 4), and “koinozyme” (5). It is probably part of a multi-enzyme membrane particle(S). It is not clear whether all these terms refer to the same API, or whether the appearance of a particulate API is connected specifically with cholestasis. There is evidence for another high-molecular-mass API, seen in cases of malignant liver disease (6). These two forms can be separated by electrophoresis on a cellulose acetate membrane; the “pathological biliary” isoenzyme migrates fast cathodically (API Vp), whereas the form seen in malignant liver diseases remains at the origin (API ifi) (4,7). The increased API in the serum of rats with biliary obstruction is completely different from the API in man (8). The present study was designed to compare the diagnostic validity of the “pathological biiary” isoenzyme (API Vp) in cholestasiswith lipoprotein-X (LP-X) and to answer the question of whether API Vp is found exclusively in biliary obstruction. There are conflicting reports that LP-X is highly specific for cholestasis (9-20). Additionally, LP-X reportedly occurs in some connection with, or perhaps bound in some way as a complex to, a particulate API (2, 21-23).