Long-term stability of alpha-1-antichymotrypsin complexed form of prostate specific antigen.
PSA complexed with alpha-1-anti-chymotrypsin (cPSA trade mark ) is the moiety in greatest proportion in the serum of men with prostate cancer (CAP). The performance of this analyte has been established primarily in retrospective archival serum. Studies indicate cPSA trade mark provides the specificity enhancement of the free-to-total PSA ratio, yet obviates the need to measure two markers. In the present investigation we sought to establish the stability of cPSA trade mark with long-term storage. Serum from men undergoing ultrasound-guided biopsy was utilized. Serum was assayed soon after collection and 18 months later. All serum was initially aliquotted and stored at -80 degrees C. There was no freeze-thaw. cPSA trade mark was measured utilizing the Bayer Immuno 1 method according to manufacturer's recommendations. The mean (s.d.) PSA was 5.5 (3.8) and 5.6 (3.9) ng/ml at the initial and subsequent testing, respectively. The medians were 4.3 and 4.4 ng/ml, respectively. No significant differences exist between the two determinants (r(2)=1.0, slope=1.01, t-test P=0.9194). These data establish for the first time the long-term stability of cPSA trade mark. Retrospective studies performed on archival material should give meaningful results. Prostate Cancer and Prostatic Diseases (2000) 3, 191-194