Prostate specific antigen as a predictor of an abnormal digital rectal examination

To assess the ability of serum prostate specific antigen (PSA) to predict and differentiate patients with normal and abnormal digital rectal findings.

A prospective analysis of 1374 participants in a prostate cancer screening programme was performed. After completion of a questionnaire including age and voiding symptoms as well as phlebotomy for PSA analysis, digital rectal examination was performed and the findings were categorized with respect to size, consistency, symmetry and nodularity.

In men less than 50 years of age the mean serum PSA level failed to discriminate any of the digital rectal examination categories. In men over 50 there was a statistically significant difference in mean PSA levels between symmetrical, normal sized prostates and symmetrically enlarged glands as well as between symmetrical, normal sized and abnormal prostates (P < 0.05). No statistically significant difference was found in mean serum PSA levels between symmetrically enlarged prostate glands and those with palpable nodules. PSA levels < or = 2.5 ng/ml (normal range for the Yang polyclonal assay) and < 7.4 ng/ml (corresponding to the normal range of < 4.0 ng/ml for the Hybritech monoclonal assay) demonstrated a probability of an abnormal digital rectal examination of 11% and 14% respectively. PSA levels > 18.4 ng/ml (corresponding to monoclonal levels of > 10 ng/ml) had a 67% probability of an abnormal digital rectal examination. However, moderate elevations in PSA could not be used to predict digital examination abnormalities due to the high incidence of moderate PSA elevations associated with symmetrical enlargement of the prostate.

Serial annual PSA measurements may provide an alternative means of screening men over 50 years of age. Contamination of results with PSA elevation due to benign prostatic hyperplasia remains, however, a problem.