Ultrasensitive detection of prostate-specific antigen by a time- resolved immunofluorometric assay and the Immulite immunochemiluminescent third-generation assay: potential applications in prostate and breast cancers

We report an ultrasensitive time-resolved immunofluorometric assay (TRIFA) for prostate-specific antigen (PSA). The assay is an improvement of our previous report (Clin Chem 1993;39:2108-14) and includes the utilization of two monoclonal antibodies and a one-step incubation period, which greatly reduces analysis time. The new method demonstrates a superior lower analytical limit of detection (< or = 1 ng/L), a wide dynamic range, absence of a hook effect at 10(6) ng/L PSA, and equimolarity for free PSA and PSA-antichymotrypsin complex. Also, we have compared several aspects of our TRIFA with a commercially available third-generation assay (Immulite). An evaluation of breast tumor cytosol extracts from 315 patients shows PSA immunoreactivity > 15 ng/g of total protein in 28% and 23% by TRIFA and Immulite analysis, respectively. Both methods demonstrate a significant association between breast tumor PSA immunoreactivity and progesterone and estrogen receptor positivity (P