Evaluation of an immunoradiometric assay protocol for determining prostate-specific antigen

Abstract

The levels of Lower Limit of Detection (LLD) and the Biological Detection Limit (BDL) for prostate-specific antigen (PSA) by an assay system are essential for successful prediction of recurrent disease after radical prostatectomy. A study was conducted to evaluate an Immunoradiometric Assay (IRMA) system to establish the LLD and BDL for PSA. The IRMA was validated by Recovery and Dilution experiments, where standard quantities of purified free-PSA (f-PSA) and PSA complexed to α₁-antichymotrypsin (PSA-ACT) were added to sera from healthy subjects and patients harbouring prostate cancer. The dilution and recovery experiments revealed an over-recovery for f-PSA (112.4 ± 12.4 %) and an under-recovery for PSA-ACT (86.4 ± 13.6 %). Six pools of zero standard and sera from 6 radical prostatectomy patients (with no histopathological evidence of relapse) were analysed in 20 replicates by the IRMA system, and the LLD and BDL values determined were 0.11 ng mL^-1 and 0.34 ng mL^-1 (within the standard ranges of 0.03 - 0.11 ng mL^-1 and 0.06 - 0.83 ng mL^-1 respectively). The results indicated satisfactory evaluation, and the data generated with the IRMA protocol was reliable.