為評估前列腺特異抗原密度(PSAD)是否可增加前列列特異抗原(PSA)用於區分前列腺癌與良性前列腺肥大的價值，我們利用從民國82年4月到民國85年1月在台大醫院泌尿部接受前列腺手術的病人來作回溯性分析。在517例PSA值小於50 ng/mL的病人中有50例經病理診斷為前列腺癌，而另外467例則為良性前列腺肥大，這兩組病人其PSA與PSAD的平均值有顯著的差異性(P值都小於0.001)。若根據PSA值將這些病人細分為4組(PSA: 0-4.0 ng/mL; 4.1-10.0 ng/mL; 10.1-20.0 ng/mL; 20.1-50.0 ng/mL)來做分析，則在PSA為4.1-10.0 ng/mL10.1-20.0 ng/mL這兩組病人，PSAD區分前列腺癌及良性前列腺肥大的能力明顯優於PSA，至於在另外二組病人(PSA 0-4.0 ng/ml與20.1-50.0ng/ml)，PSA與PSAD則無此差別。 根據上述的結果，我們再進一步分析使用PSAD於血清PSA值為4.1-20.0ng/ml的病人時，其區分前列腺癌與良性前列腺肥大症的敏感性(sensitivity)與特異性(specificity)，若以PSAD值為0.15為分界點，則其敏感性為85%而特異性為22%，若將PSAD值提高到0.20，則其敏感性為80%而特異性為48%，由這個研究結果，我們認為對於血清PSA值介於41-20.0ng/ml間的病人而言，使用PSAD來區分前列腺癌與良性前列腺肥大的能力雖然優於PSA，但是其偏低的特異性卻阻礙了其臨床上的實用價值。

To evaluate if prostate specific antigen density (PSAD), the ratio of serum PSA level to volume of prostate, can enhance the ability of PSA in differentiating prostatic adenocarcinoma (PCa) from benign prostatic hyperplasia (BPH), a retrospective study was conducted on patients having undergoing prostatic operations in our institution between April 1993 and Janurary 1996. Of the 517 patients with a preoperative serum PSA level <50 ng/Ml, 50 were documented to be PCa and 467 were to be BPH. There were significant differences in both the mean PSA (20.5 vs. 7.2 ng/mL, P<0.001) and the mean PSAD (0.94 vs. 0.21, P<0.001) values between patients with PCa and those with BPH. These patients were then divided into 4 groups according to their serum PSA levels (PSA: 0-4.0 ng/mL; 4.1-10.0 ng/mL; 10.1-20.0 ng/Ml; and 20.1-50.0 ng/mL) and patients with PCa and those with BPH were compared in each group with respect to the values of PSA and PSAD. PSAD was significantly better than PSA in differentiating PCa from BPH in the group with serum PSA level of 4.1 to 10.0 ng/mL (P<0.0001 vs. P=0.69) and in that with a serum PSA level of 10.1 to 20.0 ng/mL(P<0.0001 vs. P=0.82). Subsequently, the diagnostic efficacy of PSAD in distinguishing PCa from BPH in patients with a serum PSA of 4.1 to 20.0 ng/mL was evaluated. By using PSAD of 0.15 as a cutoff point, the sensitivity in differentiating PCa from BPH was 85%, the specificity was 22%, and the positive predictive value was 9%. Raising the cutoff value to 0.20 resulted in a sensitivity of 80%, a specificity of 48% and a positive predictive value of 12%. We conclude from this study that although PSAD could better discriminate between PCa and PBH in patients with a serum PSA of 4.1 to 20.0 ng/mL than PSA, its clinical value when used alone is limited by its imperfect specificity and positive predictive value.