[Value of commercial enzyme immunoassays in the determination of prostatic acid phosphatase].

In 261 non-selected patients (190 prostate adenoma, 71 carcinoma of prostate) prostatic acid phosphatase (PAP) was measured prior to treatment using three different commercial enzyme immuno assays. According to the normal values given by the manufacturers we found different specificities (ranging from 0.61-0.88) and sensitivities (0.45-0.75). However, the receiver-operating-characteristics-curves (ROC) for each of the tests were similar. Since we observed a considerable overlapping of PAP-activity measured in patients with prostatic adenoma and carcinoma we tried to optimize the specificity of the three assays. The actual cut-off value was determined by use of a tangent with the "a posteriori prevalence" (adenoma:carcinoma = 190:71 = 2.6) on each ROC-curve. With this method we found a similar range of sensitivity (0.38-0.48) and specificity (0.96-0.97). The use of a cut-off-value according to the "a posteriori prevalence" results in optimizing of sensitivity and specificity by taking into account the specific long term distribution of prostate adenoma/carcinoma in the respective material.