PURPOSE: We determined the effect of digital rectal examination and prostatic
biopsy on serum total and free prostate specific antigen (PSA) concentrations in men
undergoing screening for prostate cancer.
MATERIALS AND METHODS: In 93 men recruited from our PSA screening program we
measured the serum concentrations of total and free PSA on 3 occasions during a 30-day
interval before performing digital rectal examination. Total and free PSA measurements were
repeated 1 and 24 hours after the rectal examination. Serum total and free PSA also was
measured immediately before, and 1 hour, 24 hours and 1 week after prostatic biopsy in 30
men.
RESULTS: Biological variation for total and free PSA was 14.7 and 14.0%,
respectively. At 1 hour after rectal examination total and free PSA increased by more than
the biological variation in 31 and 48% of the men, respectively. Increases were
significantly greater in men whose initial PSA concentrations were less than 4.0 ng./ml.
There was a dramatic increase in total and percentage of free PSA in all men 1 hour after
prostatic biopsy. Increases in percentage of free PSA were greater in men whose biopsies
revealed cancer. Total PSA remained elevated for at least 1 week in most men, while
percentage of free PSA returned to within or less than the biological variation of the
baseline level in 90% of the men by 24 hours.
CONCLUSIONS: Digital rectal examination causes a modest increase in total and
percentage of free PSA. Prostate needle biopsy causes more dramatic increases in both forms
of PSA. Free PSA is preferentially released into the serum after prostatic manipulation and
appears to be cleared more rapidly than complexed PSA. The differential return of the
different PSA forms to baseline levels after biopsy could affect the use of measurements of
the percentage of free PSA in clinical practice.
