This study investigated the serum prostate-specific antigen concentration in 100 healthy men (mean age, 26.3 years; range, 20-29 years) with a clinically normal prostate gland. The effect of digital rectal examination and ejaculation on the serum concentration, and the variability of the serum concentration over 1-week and 1-month periods were examined. In the 100 subjects, the serum prostate-specific antigen concentration ranged from less than 0.1-2.6 ng/ml. The mean, median, and mode were 0.68 ng/ml, 0.6 ng/ml, and 0.4 ng/ml, respectively. The 97.5th percentile value was 2.1 ng/ml. The mean and median changes in the serum concentration after digital rectal examination were -0.013 ± 0.11 ng/ml and 0.0 ng/ml, respectively (P = 0.59 compared with control group). The mean change after ejaculation was 0.05 ± 0.12 ng/ml, and the median change was 0.0 ng/ml (P = 0.14 compared with control group). Diurnal variation showed minimal change in 16 patients over a 1-week period. The mean change (p.m. value - a.m. value) was 0.003 ng/ml (range, -0.2-0.06 ng/ml). In addition, the serum concentration showed minimal intrapatient variability in 20 patients throughout a 1-month period; the average coefficient of variation (standard deviation/mean) in these subjects was 16.5% (range, 6.4-45.2%). These results indicate that the range in the serum concentration of prostate-specific antigen for healthy men with a clinically normal prostate gland is significantly lower (0.0-2.6 ng/ml) than the currently employed range (0.0-4.0 ng/ml; Tandem-R PSA assay); in addition, digital rectal examination and ejaculation have no significant effect on the serum concentration. Finally, the time of day has little effect, and the variability in the serum concentration of prostate-specific antigen over a 1-week and 1-month interval is minimal.
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