In pursuit of the abnormal serum alkaline phosphatase

The serum alkaline phosphatase (ALP) is often included among the tests used for case-finding among ambulatory patients. To determine the positive predictive value of the ALP, test results for all adults screened by a health maintenance organization between March and December 1969 were obtained by computer. The authors reviewed the charts of all 661 patients with abnormal tests whose primary source of medical care was at this facility. Complete two-year follow-up data were available for 91% of these patients. There were 56 patients (9%) with a diagnosis that could have explained an abnormal ALP. Of those cases in which ALP would have been clinically useful all but one could have been diagnosed by a simple, noninvasive work-up, and in that one case, no management change would have occurred. The authors conclude that in the absence of a small number of specific indications, extensive testing need not be performed to evaluate an isolated abnormal ALP obtained from a screening examination. Received from the Department of Medicine and the School of Public Health, University of California, Los Angeles, Los Angeles, California. Supported in part by the Robert Wood Johnson Clinical Scholars Program. The views expressed herein do not necessarily represent those of the Robert Wood Johnson Foundation.