The ease of calibration and the accuracy of free PSA assays in comparison with assays of the PSA-ACT complex suggest that measurements of free to total PSA most accurately reflect the inverse of the proportion of PSA complexed to ACT in serum. Results: The mean age of the entire population was 63.6 years (range 35 to 86). Abnormal digital rectal examination findings were present in 33.4% of the patients. The mean and median values of PSA and cPSA were significantly higher and the F/T PSA ratio was lower in patients with prostate cancer. Over the past years, the assessment of equimolarity has been typically performed by the characterization of the recovery of IS 96/670, consisting of 90% PSA-ACT and 10% PSA free form, by marketed PSA assays. In addition, previous attempts to measure complexed PSA (PSA±ACT: PSA bound to a-1-antichymotrypsin) have been limited to the high cross reactivity of the monoclonal antibodies to other ACT Comparison of the clinical value of complexed PSA and total PSA in the discrimination between benign prostatic hyperplasia and prostate cancer Authors Michael Froehner 1 , Oliver W Hakenberg , Rainer Koch , Uta Schmidt , Axel Meye , Manfred P Wirth Affiliation Many studies have explored the effect of free/total prostate-specific antigen (f/t PSA) ratio in monitoring prostate cancer. We conducted a meta-analysis to identify the accuracy of the f/t PSA ratio in the diagnosis of prostate cancer in patients who have PSA levels of 4 to 10 ng/mL. The total, free and complexed PSAs increased with age (linear trend, p < 0.001), but the percent free and complexed PSA and the free/complexed PSA did not change significantly with age. Total PSA GM increased from 0.74 μg/l, for men 40-49 years, to 1.82 μg/l for men 80 years and older. We selected serums from 51 fully characterized prostate cancer patients and 48 biopsy-proven BPH patients in order to test the ability of the ratio of the free/total PSA in distinguishing between CaP and BPH patients in the best case scenario. The 51 cancer patients had cancer volumes ranging from 2.0-17.8 mL and had a median % free PSA of 8.9%. Complexed PSA: This test directly measures the amount of PSA that is attached to other proteins (the portion of PSA that is not "free"). This test could be done instead of checking the total and free PSA, and it could give the same amount of information, but it is not widely used. Prostate specific antigen (PSA) exists in the serum in several molecular forms that can be measured by immunodetectable assays: free PSA, PSA complexed to alpha 1-antichymotrypsin (complexed PSA) and total PSA, which represents the sum of the free and complexed forms. sAgDW.