Comparative performance of three radioimmunoassays for prostatic acid phosphatase

Three commercial radioimmunoassays and one enzymatic assay for prostatic acid phosphatase (PAP) have been tested on 122 patients to determine their relative specificity, sensitivity, and diagnostic value. Each of the three radioimmunoassays was found to have special merits. For distinguishing Stage IV prostatic cancer from normal patients without prostatic disease, the Smith Kline (SKF) and New England Nuclear (NEN) assays provide more significant differences. The SKF test also best distinguishes all stages of prostatic cancer from benign prostatic hyperplasia (BPH), but is inferior to the Malinckrodt (MAL) assay for contrasting Stage IV prostatic cancer from BPH. Values obtained with the NEN assay best distinguish the stages of prostatic cancer. Only with the MAL assay are significantly higher PAP values obtained in patients with metastases to bone than those without positive bone scans. Viewed from the point of sensitivity, the SKF assay proves best at all levels of specificity examined in detecting all stages (I-IV), and Stage IV prostatic cancer. By none of the assays can estrogenized Stage III and IV cancer patients be distinguished from those not on estrogen.