為了評估血清游離前列腺特異抗原比例在血清總前列腺特異抗原濃度介於4.0 -10.0 ng / ml的病人時，對於區別良性前列腺疾病與前列腺癌上的臨床角色。從221 位血清總前列腺特異抗原濃度介於4.0-10 .0 ng/ml 的男性病人中，總共43位病人進入本試驗。這43位病人除了接受肛門指診和經直腸前列腺超音波檢查外，都有病理檢驗報告，其中27位病人接受經直腸前列腺超音波切片檢查，16病人因為阻塞性排尿症而接受經尿道前列腺切持除手術。所有病人的血清檢驗總前列腺特異抗原濃度均介於4 .0-10.0 ng / ml（Tandem-E®, Hybritech, Inc, San Diego CA）時，立即置於-70°C的冰箱儲存。另外，用另一種放射免疫分析方法來測定血清游離前列腺特異抗原濃度及第二次的血清總前列腺特異抗原濃度( PSARIACT & FPSA-RAICT, CIS, Biointemational, France）。我們分別比較兩種不同方法測量出來的血清游離前列腺特異抗原比例。在這43位病人中包括34個前列腺肥大（79.1 % )，5 個前列腺炎（11.6 %）及4個前列腺癌（9.3 %）。利用兩種不同之分析方法他們的血清游離前列腺特異抗原比例分別為28.0% ± 12.2 %，23.6% ± 9.1 %，8.7% ± 1.3% ( FPSA-RIACT/Tandem-E®）與29.6% ± 13.1%，28.5% ± 13.1%，9.7% ± 1.1% ( F PSA-RIACT/PSA-RIACT）。前列腺癌病人比前列腺炎及前列腺肥大的病人有比較低的血清游離前列腺特異抗原比例（p值為0.015及0.003）。然而，在前列腺炎與前列腺肥大的病人之間血清游離前列腺特異抗原比例則無明顯差別。此外，以兩種不同方法測量出來的血清游離前列腺特異抗原比例有很好的相關性（r2 = 0.90）。血清游離前列腺特異抗原比例可用來幫助區別血清總前列腺特異抗原濃度介於4.0-10.0 ng/lnl 之問的良性前列腺疾病與前列腺癌病人，以避免不必要的生檢切片。同時在決定游離前列腺特異抗原比例時，不需要再次檢驗血清總前列腺特異抗原濃度。

To explore the role of percent free-prostate specific antigen(PSA) on the differentiation between benign and malignant prostatic diseases in patients with serum total PSA levels between 4.0 and 10.0 ng/ml. Forty-three out of the 221 screened men who had total PSA levels between 4.0 and 10.0 ng/ml were retrospectively enrolled into this study. in addition to digital rectal examination(DRE), transrectal ultrasonography(TRUS), and total PSA, they received either TRUS-guided biopsies(n=27) or transurethral resection of the prostate (TUR-P) (n=16). All sample sera were then stored at -70 °C after the initial measurement of total PSA levels using an immunoenzymometric assay(Tandem-E®, Hybritech). Thereafter, all stored sera were quantified for free-PSA levels and total PSA levels using a different radioimmunometric assay(PSA-RJACT, CIS). Two values of percent free-PSA were obtained for each individual by dividing the same free-PSA level by 2 different total PSA values as measured by 2 different assays. Among the 43 patients, there were 34(79.1%) patients with benign prostatic hyperpla-sia(BPH), 5(11.6%) with prostatitis, and 4(9.3%) with prostate cancer(PC). Using these 2 different total PSA assays, the percent free-PSA in patients with BPH, prostatitis, and PC were 28.0%±12.2%, 23.6%±9.1%, 8.7%±1.3% (FPSA-RJACT/Tandem-E®) and 29.6%±13.1%,28.5%±13.1%, 9.7%±1.1% (FPSA-RJACT/PSA-RIACT), respectively. Patients with PC had significantly lower values of percent free-PSA (less than 12%) while those with either BPH or prostatitis had values greater than l2%(p values, 0.015 and 0.003, unpaired t-test). In contrast, the percent free-PSA values were not statistically different between BPH and prostatitis patients in both assays (p=0. 44, unpaired t-test). Besides, the correlation between the 2 values of percent free-PSA was good(r2 =0.90), based on 2 different assays for total PSA levels. Our study implies that percent free-PSA can help differentiate prostate cancer from benign prostatic diseases, and thus greatly reducing unnecessary biopsies. There is no need to measure the total PSA levels again while determining the percent free-PSA.