Storage stability of prostate-specific antigen

The in vitro stability of prostate-specific antigen (PSA) at -20 degrees C was examined in a prospective study. After a storage interval of 20 to 42 months (mean 32 months), a mean decline in the PSA concentration of only 0.6% was found. The coefficient of correlation was 0.99. The PSA concentrations of the 128 sera (minimum 0.1, maximum 1120 ng/ml) were determined with a monoclonal equimolar immunoenzymatic assay (Tandem (R)-E, Hybritech). Neither the interval of storage, nor the diagnosis, nor the absolute value of PSA concentration showed significant influence on stability. As shown in the literature, PSA is stabil at room temperature for 24 to 96 hours. For longer storage intervals (up to several years), a storage temperature of -20 degrees C is necessary. The immunoenzymatic assay used allows reliable determination of PSA concentrations over a wide range of concentrations.