Evaluation of a monoclonal antibody-based immunoradiometric assay for prostatic acid phosphatase

This report evaluates a new immunoradiometric assay for prostatic acid phosphatase in serum, based on a dual monoclonal antibody reaction system (Hybritech-TANDEM). A solidphase antibody binds the acid phosphatase molecule and a second monoclonal antibody to a different antigenic site serves as the 125I-radiolabel. The method was tested on 67 patients with various stages of prostatic carcinoma and 134 patients without the disease. It also was compared with a conventional polyclonal radioimmunoassay (NEN) and an enzymatic activity method (duPont aca). The upper limit for the TANDEM assay on nondiseased male patients was found to be 2.0 microgram/L. Based on this upper limit of normal, the diagnostic sensitivity of the method for all cases of prostatic carcinoma was 60%. We could not distinguish the enzyme released in abnormal amounts due to benign prostatic hypertrophy and certain nonprostatic malignant diseases from that of prostatic carcinoma. The diagnostic specificity was calculated at 95%. For the clinically undetectable Stage 1 disease, sensitivity was 44% (four abnormal values out of nine cases). The TANDEM procedure is simple to use and reproducible.