Hybritech Total and Free Prostate-specific Antigen Assays Developed for the Beckman Coulter Access Automated Chemiluminescent Immunoassay System: A Multicenter Evaluation of Analytical Performance

Previously reported clinical trials have shown that measurement of the different forms of prostate-specific antigen (PSA) (1) is useful in the differentiation of prostate cancer from benign prostatic conditions. Men with prostate cancer tend to have lower percent free PSA (%FPSA) values than men with benign disease (2)(3)(4); %FPSA is the ratio of free PSA to total PSA times 100%.Beckman Coulter, Inc. (Fullerton, CA) has developed the Access Hybritech PSA and Hybritech PSA assays for use on the automated Access Immunoassay System. The assays are two-site immunoenzymatic (“sandwich”) assays that use mouse monoclonal antibody in alkaline phosphatase conjugate and paramagnetic particles coated with a second mouse monoclonal antibody. After unbound particles are removed by washing, a chemiluminescent substrate, Lumi-Phos 530,1 is added to produce light directly proportional to the amount of analyte in the sample as determined from a stored calibration curve. Calibrators are assigned up to 150 μg/L PSA and 20 μg/L FPSA.Analytical performance of the new assays was evaluated at four clinical laboratories located in the United States and at the manufacturer’s laboratories. Proficiency of the Access instruments and operators was demonstrated by assaying an identical panel of 18 human samples. Serum aliquots were stored at −70 °C, shipped frozen, and tested in duplicate over 2 days on both the Access and the reference Tandem methods. Proficiency panel results from each laboratory were analyzed by Deming regression and compared with the values assigned by the manufacturer. Each laboratory achieved results within 10% of the target values before proceeding. For the remainder of the study, Lyphochek Immunoassay Plus Control2 and Access QC control with ranges assigned for the Access instrument for each assay were used daily to verify calibration of individual instruments and accurate sample recovery from stored calibration curves. Controls …