Serum prostatic acid phosphatase (PAP): monoclonal enzyme-linked immunoassay compared to polyclonal radioimmunoassay

A new enzyme linked immunosorbent assay (ELISA) kit which utilizes a monoclonal antibody against prostatic acid phosphatase (PAP) was compared with current radioimmunoassay (RIA) methodology which uses a polyclonal antibody. Both assays are double antibody immunoassays with the major difference being the method of antibody preparation. A study of intrarun precision using control material showed an average within run coefficient of variation (CV) percent as 7.0 percent and 6.9 percent for ELISA and RIA, respectively, while between run CV percent averaged 11.1 percent and 11.5 percent, respectively. Thus, precision results compare similarly between the two assays. The specificity showed significantly different results. Patterns of correlation between the two methods indicate differing specificities of the primary antibodies. The values for ELISA were greater than RIA for control sera and patient samples when values fell outside the reference range; however, RIA values exceeded ELISA values with patient samples which fell within the reference ranges as provided by each manufacturer. Therefore, there exists a question of specificity of antibody employed in each of the two assays. The PAP antigen is prepared from two different sources for each kit. The ELISA manufacturer prepares antigen from seminal fluid and RIA manufacturer prepares antigen from normal human prostate. The question of specificity may be influenced by: (1) source of antigen used in immunizing animals and (2) monoclonal versus polyclonal means of producing antibody.