In pursuit of the abnormal serum alkaline phosphatase: a clinical dilemma.

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 workup, 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.