[Free/total ratio of prostate-specific antigen (PSA) for prostate cancer detection in patients with gray zone PSA level].

Thirty seven patients complaining of voiding disturbance who showed gray zone total prostate-specific antigen (t-PSA) level (upper limit of normal approximately 10 ng/ml) but did not reveal apparent cancerous findings in the prostate were examined for free PSA (f-PSA) and prostate volume. According to histological diagnosis, 9 were cancer cases and the other 28 were non-cancer cases. The free/total (F/T) ratio was 0.10 and 0.16 in the cancer and non-cancer groups, respectively (t-PSA; DPC kit, p = 0.03). The t-PSA (DPC and Dinabott kits), f-PSA and PSA density alone did not distinguish these two groups. For diagnosis of cancer, the ratio seemed to be F/T, the most reliable followed by PSA density and t-PSA. When using a 13% F/T, the sensitivity and specificity for cancer detection were 88.9 and 70.8%, respectively. t-PSA measured with the Dinabott kit, showed a similar tendency except that the F/T ratio showed a slight variation. Prostate volume and patient age influenced the F/T slightly, but these factors may not impair the usefulness of F/T.