To examine the effectiveness of prostatic acid phosphatase and creatine kinase-BB determinations in detecting prostatic cancer serum from 594 men more than 40 years old was assayed for prostatic acid phosphatase with the thymolphthalein monophosphate substrate and a radioimmunoassay kit. Creatine kinase-BB levels also were measured with a radioimmunoassay kit. Patients with benign prostatic hyperplasia had higher prostatic acid phosphatase levels than normal controls. Accordingly, to avoid a high incidence of false positives in patients with benign prostatic hyperplasia the 92.5 percentile level of the patients with benign prostatic hyperplasia (3.9 ng/ml) was chosen as the upper limit of normal. With this critical value elevated prostatic acid phosphatase levels were observed in 6% of the patients with clinical stage A disease, 8% with stage B, 35% with stage C and 68% with stage D. The radioimmunoassay was no more effective than the enzymatic assay in detecting prostatic cancer. A correlation between prostatic acid phosphatase levels and patient race was observed, with 80% of the black patients with extracapsular prostatic cancer having elevated prostatic acid phosphatase levels compared to 34% of the white patients with similar stage disease. Creatine kinase-BB was elevated only in patients with advanced disease and was of little value in the diagnosis of prostatic cancer.
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