Measurement of serum prostate specific antigen using IMx prostate specific antigen assay

The analytical characteristics of singlet determinations of the IMx prostate specific antigen (PSA) assay are similar to the mean of duplicates using the Tandem-R PSA assay. The 2 assays are standardized equally and provide test results that correlate well (r = 0.9997). The IMx PSA assay is more automated, requires less technologist time and provides faster test results. This assay has a minimal detection limit of 0.02 to 0.04 ng./ml. and functional sensitivity at a 20% coefficient of variation of 0.06 to 0.13 ng./ml. With a sensitive lot of IMx PSA reagents, only 38% of postradical prostatectomy patients had nondetectable values compared to 60% with the Tandem-R PSA assay. The within-person, biological standard deviation of PSA concentrations in post-radical prostatectomy patients was 0.01 ng./ml. Therefore, with a sensitive assay these low concentration measurements should be reliable for monitoring. However, the clinical use of these low concentrations for early detection of tumor recurrence must await further studies.