Kinetics of postbiopsy levels of serum free prostate-specific antigen and percent free prostate-specific antigen.

Objectives: We evaluated the effects of transrectal ultrasound-guided biopsy of the prostate on serum total and free prostate-specific antigen (PSA) and the free/total PSA ratio and factors affecting variations in PSA levels.

Methods: Serum total and free PSA levels and the free/total PSA ratio were determined in 48 men (mean age 66+/-7 years) before and 1 hour, 8 days, and 30 days after prostate biopsy. At least six cores were taken using a biopsy gun with an 18-gauge needle. The coefficient of variation of PSA was calculated as the postbiopsy/prebiopsy PSA ratio. Changes in PSA levels and the coefficient of variation were studied.

Results: Fifteen (31%) of 48 men had adenocarcinoma on biopsy. Total and free PSA values were significantly increased 1 hour and 8 days after biopsy, and both returned to baseline 30 days after biopsy. The free/total PSA ratio was significantly increased (55%) 1 hour after biopsy and significantly decreased (12%) 8 days after biopsy. Thirty days after biopsy, the median of the free/total PSA ratio (18%) was not significantly different from the prebiopsy ratio (16%). The median of the coefficient of variation of the free/total PSA ratio was 3, 0.7, and 1 at 1 hour, 8 days, and 30 days after biopsy, respectively. Age, prostate volume, number of cores, and digital rectal examination and histologic findings were not significantly associated with variation in percent free PSA. Variation in percent free PSA at day 8 was associated with prebiopsy total PSA value and the free/total PSA ratio.

Conclusions: Prostate biopsy dramatically alters the percent free PSA. The free/total PSA ratio was decreased 8 days after biopsy and returned to prebiopsy levels in 75% of patients at 1 month after biopsy. Measurement of free PSA levels and the free/total PSA ratio should not be done within 4 weeks of prostate biopsy.