A new endogenous immunoenzyme assay for prostatic acid phosphatase evaluated.

I evaluated the performance of the "ORTHO PAP-IA," an endogenous immunoenzyme assay for prostatic acid phosphatase. The procedure is based on double-antibody precipitation of the antigen, followed by quantification of its enzymic activity. The antibodies are in large excess, to speed the reactions and minimize sensitivity to variations in assay conditions. Enzymic activity is measured via an extremely sensitive colorimetric reaction, the analytical sensitivity of which exceeds that of radioimmunoassay. Absorbance is linearly related to activity concentration up to an absorbance of 4.0, and only a single calibration standard is required. Within-run CV was less than 2%, between-run CV about 4%. Neither individual blanks nor assay in duplicate is required. All reagents, including the enzyme standard, are stable solutions. Results correlated well with those by a standard radioimmunoassay (r = 0.993, n = 38).