Rg. Nixon et al., DAY-TO-DAY CHANGES IN FREE AND TOTAL PSA - SIGNIFICANCE OF BIOLOGICALVARIATION, PROSTATE CANCER AND PROSTATIC DISEASES, 1(2), 1997, pp. 90-96
In this study we evaluated the physiological variation of free and tot
al prostate-specific antigen (PSA) levels to determine how the percent
free/total PSA was affected. Twenty four patients had blood drawn for
ten consecutive weekdays. The percent coefficient of variation (% CV)
of biological variation was calculated. The results were log-normally
distributed with geometric means of 12.0% CV, 7.3% CV, and 8.8% CV fo
r free, total, and percent free/total PSA, respectively. When applied,
the percent free/total, PSA would need to fluctuate by 31% to indicat
e that a significant change (critical difference, P<0.05) between two
measurements had occurred. Biological variation of PSA measurements is
substantial.