Significance of elevated liver alkaline phosphatase in serum

The serum alkaline phosphatase was fractionated by polyacrylamide gel electrophoresis in 317 patients with elevated serum alkaline phosphatase activity. In 253 patients the source of the elevation was the isoenzyme of presumed liver origin, band L. In 87 of these patients, there was either no obvious liver disease or the alkaline phosphatase elevation was inappropriately high. In 19 of the 87, liver disease was further excluded by liver biopsy or by laparotomy. Because of this, biochemical studies were done to verify the hepatic origin of band L. Band L and alkaline phosphatase extracted from human liver migrated together on polyacrylamide gel electrophoresis before and after digestion with Vibrio cholerae neuraminidase. They had identical pH optima, sedimentation coefficients, Michaelis constants, and rates of inactivation at 55.5 degrees C. They had different rates of inactivation in 3 M urea. Over-all, the data indicate that band L is of liver origin, and that elevation of the hepatic alkaline phosphatase isoenzyme may be a nonspecific finding in certain patients.