Radioimmunoassay for prostatic acid phosphatase helps discriminate patients with prostatic cancer

We measured serum prostatic acid phosphatase in ostensibly normal controls and a selected patient population, using both a modified radioimmunoassay and an enzymic method with thymolphthalein monophosphate as substrate. The upper limit of normal for the radioimmunoassay was 2.2 micrograms/L; its sensitivity and specificity for prostatic cancer were 71 and 95%, respectively, vs 51 and 99% for the enzymic method. For both methods the correlation between clinical staging and values for acid phosphatase was poor. Our data suggest that adjunctive use of the radioimmunoassay may help further discriminate those patients requiring needle biopsy.