Measurement of prostate-specific antigen in serum using four different immunoassays

This paper summarises the results of a comparison of the Serono SR1, Ciba Corning ACS 180, Abbott IMx and Hybritech Tandem-R prostate-specific antigen assays. One hundred serum pools were assayed using the four methods. Linear regression analysis of the data showed that, although overall correlations were good, different assays gave different prostate-specific antigen concentrations. Tandem-R and SR1 assays gave very similar prostate-specific antigen values; in general, the ACS assay gave higher prostate-specific antigen values than the IMx assay gave lower prostate-specific antigen values than the established Tandem-R assay. Following fractionation of serum from prostate cancer patients, all immunoassays detected several immunoreactive prostate-specific antigen forms. The major immunoreactive form (> 88% of immunoreactivity) had an apparent molecular size of M(r) approximately 100,000 and is likely to be a complex of prostate-specific antigen with alpha 1-antichymotrypsin; two minor forms had apparent molecular sizes of M(r) approximately 30,000 (probably free prostate-specific antigen) and 200,000 (probably prostate-specific antigen complexed to high molecular mass anti-proteases). From this study there is no evidence that polyclonal/monoclonal antibody immunoassays are to be preferred to monoclonal/monoclonal antibody immunoassays for the determination of free prostate-specific antigen in serum.