Diagnostic accuracy of four assays of prostatic acid phosphatase. Comparison using receiver operating characteristic curve analysis.

We compared the diagnostic characteristics of four assays of prostatic acid phosphatase by two methods. In the first analysis, receiver operating characteristic (ROC) curves were developed and the areas under the curves were calculated. In the second analysis, the sensitivity of each assay was compared with the sensitivities of the other assays with specificities set at equal levels. One or more assays were performed in 1,298 patients; 141 underwent all four assays. Pairwise comparisons of the areas under the ROC curves showed no significant differences. No differences were found in the sensitivities of the four assays when the upper limits of normal were selected to provide equal specificities. We conclude that there is little difference in diagnostic accuracy among the prostatic acid phosphatase assays. Our findings contrast with previous studies that used only one upper limit of normal and that found some assays to be superior to others. Receiver operating characteristic curve analysis corrects for the bias introduced by the choice of an upper limit of normal.