Long-term stability of alpha-1-antichymotrypsin complexed form of prostate specific antigen

Abstract

PSA complexed with alpha-1-anti-chymotrypsin (cPSA™) 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™ 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™ 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°C. There was no freeze–thaw. cPSA™ 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 (r²=1.0, slope=1.01, t-test P=0.9194).

These data establish for the first time the long-term stability of cPSA™. Retrospective studies performed on archival material should give meaningful results.