THE RATIO OF FREE TO TOTAL SERUM PROSTATE-SPECIFIC ANTIGEN AND ITS USE IN DIFFERENTIAL-DIAGNOSIS OF PROSTATE CARCINOMA IN JAPAN

BACKGROUND, To improve the clinical usefulness of prostate specific an tigen (PSA), unique methods have been proposed. The percentage of free PSA in serum facilitates the distinction between benign histologic co nditions and prostate carcinoma while retaining high sensitivity. METH ODS, Using monoclonal antibodies, an AIA total PSA assay system was es tablished that recognized PSA equally in free or complex form. The cli nical usefulness of the ratio of two different molecular forms of PSA was investigated using 268 archival serum samples. RESULTS, Men with p rostate carcinoma had significantly lower ratios of free to total PSA than those with benign prostatic hyperplasia (BPH) (P = 0.0001). At to tal PSA levels between 2.1 and 10 ng/mL, medians of total PSA were not significantly different between men with prostate carcinoma and men w ith BPH. Differences in median percentages of free PSA for these two g roups were statistically significant (P = 0.0001). The ratio of free t o total PSA was useful for identifying prostate carcinoma in palpably benign glands with total PSA of 2.1-10 ng/mL (P = 0.0001), whereas tot al PSA was not useful for such identification. When calculated for low total PSA levels between 2.1 and 4 ng/mL, sensitivity and specificity were 91.7% and 72.2%, respectively, with a cutoff value of 17%. This ratio of free to total PSA was as useful as PSA density in receiver-op erating curve analysis. CONCLUSIONS, The use of the ratio of free to t otal PSA renders total PSA of greater use for distinguishing prostate carcinoma and is applicable to patients with low total PSA. Elderly me n with a clinical diagnosis of BPH who are scheduled for surgery may b enefit from the determination of this ratio. (C) 1997 American Cancer Society.