A comparison of 4 ultrasensitive prostate specific antigen assays for early detection of residual cancer after radical prostatectomy.

The Yang Pros-Check, Abbott IMx, Tosoh AIA-PACK PA and Nichols Institute reference laboratory prostate specific antigen (PSA) assays were compared in 30 patients (138 sera) known to have no residual prostate cells. The mean + 3 standard deviations of these sera was used to define a level of PSA that would indicate residual cancer. This residual cancer detection limit for each of the 4 assays is 0.06, 0.01, 0.07 and 0.05 ng./ml., respectively, but the 0.01 level for the IMx assay is an artifact caused by setting the zero calibrator too high. All 4 assays were then used to compare the number of days from radical prostatectomy to the detection of residual cancer in 23 cases (211 sera) that ultimately failed radical prostatectomy. The Yang, Tosoh and Nichols Institute assays were all similar, with an average of 569 to 589 days. The Abbott IMx assay was relatively insensitive in detecting the first appearance of PSA after radical prostatectomy (average 821 days) and it showed the earliest detection among the 4 assays in only 1 of 23 patients.