Development and clinical evaluation of two immunoassays for prostatic acid phosphatase in serum

Polystyrene tubes were coated with IgG, isolated from antiserum against human prostatic acid phosphatase, and incubated with a known amount of purified antigen as a standard, and sera from patients. The amount of bound prostatic acid phosphatase was established by using its enzyme activity. This was performed either spectrophotometrically with p-nitrophenylphosphate (enzyme immunoassay) or fluorometrically with alpha-naphthylphosphate as a substrate (immunofluorescence assay). Results of both methods were compared with those of the conventional method and were evaluated in four groups of patients with: non-prostatic disease, hypertrophy, treated and untreated prostatic carcinoma. The first group was used to establish the upper limit of normal. In the hypertrophy group, the specificity of the immunological methods when compared with the conventional method, improved from 79% to 91%. Sensitivity, calculated from the untreated prostatic carcinoma group, was 74% for the enzyme immunoassay (EIA) and 71% for the immunofluorescence assay (IFA). The probability of having either carcinoma or hypertrophy, given observed EIA or IFA values, was calculated by the statistical method of the logistic regression.