Long-term stability of alpha-1-antichymotrypsin complexed form of prostatespecific antigen

PSA complexed with alpha-1-anti-chymotrypsin (cPSA(TM)) is the moiety in gr eatest proportion in the serum of men with prostate cancer (CAP). The perfo rmance of this analyte has been established primarily in retrospective arch ival serum. Studies indicate cPSA(TM) provides the specificity enhancement of the free-to-total PSA ratio, yet obviates the need to measure two marker s. In the present investigation we sought to establish the stability of cPS A(TM) with longterm 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 degreesC There was no freeze-thaw. cPSA(TM) w as measured utilizing the Bayer Immune 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 su bsequent testing, respectively. The medians were 4.3 and 4.4 ng/ml, respect ively. 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(TM) Retrospective studies performed on archival material should give meaningfu l results.