Radioimmunoassay of prostatic acid phosphatase: Validation and clinical application

Abstract A radioimmunoassay for prostatic acid phosphatase (PAP) has been established, using a purified preparation extracted from human seminal plasma. To obtain immunologically intact 1 25I‐PAP as a tracer, the lactoperox‐idase technique was used followed by double chromatography on Sephadex G‐50 and G‐200. The assay was sensitive, accurate and reproducible. Only leukocyte acid phosphatase cross‐reacted completely whilst acid phosphatases from other tissues (skin, lymph nodes, lung, kidney, liver, testis, platelets) did not interfere in the assay. When this method was used, PAP levels in men over the age of 20 were greater than those of women and younger men. Patients with prostatitis, benign prostatic hypertrophy (BPH) and other prostatic disorders had normal levels in more than 95% of cases. Patients who had prostatectomy for BPH had levels significantly lower than those of normal controls and those with unoperated BPH. This provides indirect evidence for the specificity of the PAP radioimmunoassay. In prostatic cancer, PAP levels measured by radioimmunoassay were more frequently and more greatly elevated with progression of the disease: 25% atstages A and B, 75% at stage C and 100% at stage D. Further, PAP measurement provided a quantitative marker to follow therapeutic response as PAP levels varied in parallel with clinical, radiologic and scintigraphic progression. Under our experimental conditions, the PAP radioimmunoassay proved to be more sensitive (percentage of increased levels in the serum of patients with prostatic cancer) and more specific (percentage of normal levels in the serum of patients with prostatic disorders other than cancer) than the enzymatic assay of these enzymes.