Biological variation of total, free and percent free serum prostate specific antigen levels in screening volunteers

Purpose: We determined the biological variation of the total, free and percent free serum prostate specific antigen (PSA) in men 50 years old or older. Materials and Methods: Between July 1995 and February 1996 we studied 84 healthy men from our PSA screening study to determine biological variation by calculating the coefficients of variation of 3 PSA measurements on blood samples drawn from each subject 2 weeks apart. Results: The mean coefficients of variation for total, free and percent free serum PSA were 15, 17 and 14%, respectively. Age, total PSA and ejaculation were not confounding factors in this analysis (that is multivariate R² less than 5% for all indexes). Conclusions: There is a mean variation of approximately 15% in measurements of total, free and percent free PSA that does not appear to be significantly affected by age and total PSA level.