THE PROPORTION OF FREE TO TOTAL PROSTATE-SPECIFIC ANTIGEN - A METHOD OF DETECTING PROSTATE CARCINOMA

BACKGROUND. Prostate specific antigen (PSA) is the most useful marker for prostate carcinoma (CaP). However, the sensitivity and specificity for PSA are not sufficient for the diagnosis of organ-confined prosta te carcinoma. Recent studies have revealed that anti-PSA antibody iden tifies both PSA complexed to alpha-1-antichymotrypsin and free PSA, wh ereas anti-gamma-seminoprotein antibody recognizes free PSA exclusivel y. To enhance the ability of PSA to detect CaP in patients with total PSA levels of 10 ng/mL or lower, we developed the ratio of gamma-semin oprotein and PSA (free/total PSA index). METHODS. We measured free/tot al PSA indices for 285 patients who had serum PSA levels of 10 ng/mL o r lower and who were diagnosed pathologically. RESULTS. Of the 285 pat ients, 228 had no prostate carcinoma (NC) and 57 had CaP. The mean tot al PSA level for CaP (5.137 +/- 2.483 ng/mL; mean +/-: standard deviat ion) was significantly greater (P < 0.0001) than that for NC (3.251 +/ - 2.129). The mean free/total PSA index for CaP (0.774 +/- 0.468) was significantly lower (P < 0.0001) than that for NC (1.563 +/- 0.938). T he sensitivity for the free/total PSA index was similar to that for to tal PSA (78.9% vs. 75.4%). However, the specificity, positive predicti ve value, and overall accuracy for the free/total PSA index (75.9%, 45 %, and 76.5%, respectively) increased by 15-20% compared with those fo r total PSA (56.6%, 30.3%, and 60.4%, respectively). CONCLUSIONS. The free/total PSA index improved the specificity of PSA without impairing the sensitivity in detecting CaP among patients with serum PSA levels of 10 ng/mL or lower. (C) 1996 American Cancer Society.