ANALYSIS OF VARIATION IN PROSTATE-SPECIFIC ANTIGEN VALUES

This retrospective study analyzes variation in prostate-specific antig en (PSA) levels in 1 29 males who were not diagnosed with prostate can cer or other known malignancies. The extent to which the assay and the biologic variation contributed to the variation in PSA concentration was evaluated from analysis of slopes characterizing PSA concentration as a function of time. The mean coefficient of variation on observati ons was 58.0 percent. The estimated mean biologic coefficient of varia tion was 55.3 percent versus a mean assay coefficient of variation of 13.2 percent, indicating that the assay variation contributed negligib ly to variation compared with the biologic variation. The concept that a PSA level which rises more than that attributable to assay variatio n indicates the need for invasive testing for prostate cancer is quest ionable. A decreasing PSA level was seen as often and of the same magn itude as an increasing level within a relatively narrow window of appr oximately one year. We are aware of no reason why this variability in PSA values would not be observed in patients with occult prostate canc er.