Diagnostic Value of Free Prostate-Specific Antigen among Men with a Prostate-Specific Antigen Level of <3.0 μg per Liter

ObjectivesThe percentage of free prostate-specific antigen (%fPSA) improves the diagnostic accuracy for prostate cancer when the serum level of total PSA (tPSA) is elevated. Approximately 14% of men with a tPSA below 3 μg/l have prostate cancer on biopsy, but the diagnostic value of %fPSA in such men is rather unknown. The purpose was to estimate the impact of %fPSA on future prostate cancer risk among men with a normal tPSA in prostate cancer screening.Subjects and methodsThe first round of the Finnish arm of the European Randomized Trial for Screening of Prostate Cancer in 1996 to 1999 comprised 20,793 men aged 55–67 yr. Screen-negative men (tPSA level below 3.0 μg/l, n = 17,680) were followed up until the end of 2003. Cumulative risk of prostate cancer was calculated as a function of %fPSA.ResultsDuring the median follow-up of 5.8 yr (range, 0–7.7 yr), 327 men were diagnosed with prostate cancer and 25% of them had a Gleason score of 7 or higher. Five years after the first screening, cumulative risk of prostate cancer was 1.7% (95%CI, 1.5–1.9%). Men with a %fPSA in the lowest quartile (<14.2%) showed a 6.9-fold risk compared with those with a level in the highest quartile (>23.7%).ConclusionsIn men with a low serum tPSA, a low %fPSA is a strong predictor of later diagnosis of prostate cancer.