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 biops y of the prostate on serum total and free prostate-specific antigen (PSA) a nd 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, a nd 30 days after prostate biopsy. At least six cores were taken using a bio psy gun with an 18-gauge needle. The coefficient of variation of PSA was ca lculated as the postbiopsy/prebiopsy PSA ratio, Changes in PSA levels and t he coefficient of variation were studied. Results. Fifteen (31%) of 48 men had adenocarcinoma on biopsy. Total and fr ee 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 rati o was significantly increased (55%) 1 hour after biopsy and significantly d ecreased (12%) 8 days after biopsy. Thirty days after biopsy, the median of the free/total PSA ratio (18%) was not significantly different from the pr ebiopsy 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 bio psy, respectively. Age, prostate volume, number of cores, and digital recta l examination and histologic findings were not significantly associated wit h 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 preb iopsy levels in 75% of patients at 1 month after biopsy. Measurement of fre e PSA levels and the free/total PSA ratio should not be done within 4 weeks of prostate biopsy. (C) 1999, Elsevier Science Inc. All rights reserved.