Different stability of free and complexed prostate-specific antigen in serum in relation to specimen handling and storage conditions

The effect of sample collection, storage conditions (time and temperature), and freeze-thaw cycles on the stability of free prostate-specific antigen (fPSA), PSA complexed with alpha (1)-antichymotrypsin (ACT-PSA), and total PSA (tPSA) in serum was studied. The analytes were quantified using immunoa ssays for tPSA and fPSA on the Elecsys system 2010 and a research assay for ACT-PSA on the ES system (Roche Diagnostics). The stability of the analyte s was calculated as percentages of the values measured in samples 1 h after blood collection. When the samples were stored at 37 degreesC, at room tem perature or at 4 degreesC, the stability of ACT-PSA was less impaired than that of fPSA. To avoid erroneous results in the determination of PSA isofor ms and their corresponding ratios, serum samples should be preserved at 4 d egreesC when the analysis is performed within 8 h after blood collection, o r they should be stored at -80 degreesC if the analysis is not feasible dur ing that period.