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 antigen (PSA), unique methods have been proposed. The percentage of free PSA in serum facilitates the distinction between benign histologic conditions and prostate carcinoma while retaining high sensitivity. METHODS Using monoclonal antibodies, an AIA total PSA assay system was established that recognized PSA equally in free or complex form. The clinical usefulness of the ratio of two different molecular forms of PSA was investigated using 268 archival serum samples. RESULTS Men with prostate carcinoma had significantly lower ratios of free to total PSA than those with benign prostatic hyperplasia (BPH) (P = 0.0001). At total PSA levels between 2.1 and 10 ng/mL, medians of total PSA were not significantly different between men with prostate carcinoma and men with BPH. Differences in median percentages of free PSA for these two groups were statistically significant (P = 0.0001). The ratio of free to 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 total 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‐operating curve analysis. CONCLUSIONS The use of the ratio of free to total PSA renders total PSA of greater use for distinguishing prostate carcinoma and is applicable to patients with low total PSA. Elderly men with a clinical diagnosis of BPH who are scheduled for surgery may benefit from the determination of this ratio. Cancer 1997; 79:90‐8. © 1997 American Cancer Society. The ratio of free to total serum prostate specific antigen (PSA) renders total PSA more useful in the diagnosis of patients with low‐range total PSA and those clinically diagnosed with benign prostatic hyperplasia.