OBJECTIVETo measure the percentage of free prostate specific antigen (fPSA) among the men without prostate diseases in Xi'an, and understand the age-related changes in percent fPSA and its association with the pathological grade and clinical stage of prostate cancer, so as to determine the reference range of percent fPSA in Chinese men.

METHODSA total of 829 men (including 775 men without prostate disease and 54 with prostate cancer) were enrolled into the study and the serum PSA and fPSA levels were measured for calculating the percent fPSA. The 775 prostate disease-free subjects were divided into 5 age groups to study the relations of PSA, fPSA and percent fPSA with age. In the 54 patients with prostate cancer, the relations of pathological grade and clinical stage with percent fPSA were investigated with reference to the related data of the men without prostate disease to establish the appropriate reference range of percent fPSA for Chinese men.

RESULTSSerum PSA or fPSA levels, but not the percent fPSA, were correlated to age. In patients with prostate cancer, the percent fPSA was also correlated to the pathological grade and clinical stage. Among the men without prostate disease we investigated, the percent fPSA was significantly lower than that reported in other countries. The reference range of percent fPSA for Chinese men was > or =15%.

CONCLUSIONThe percent fPSA is not correlated to age and has greater clinical value than PSA measurement in the detection of prostate cancer. The percent fPSA decreases in prostate cancer patients with lowered pathological grade, advanced clinical stage, and therefore increased malignancy. The reference range of percent fPSA reported in other countries does not apply to Chinese men, and according to our investigation, the reference range of percent fPSA> or =15% is appropriate for Chinese men.