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. 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. 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. An additional portion of PSA that is complexed with α 2-macroglobulin can be measured only if the complex is opened and the PSA epitopes become accessible. Of the total PSA (tPSA) in serum, 10-30% is not bound to serum proteins and is called free PSA (fPSA). 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. Complexed PSA test measures both PSA that is floating freely in the blood and PSA that is attached to other proteins in the blood. PSA levels rise with age, and men of different ethnicities may have naturally higher PSA levels, so discuss with your doctor what a healthy PSA level looks like for you. PSA, a protein produced by prostate gland cells, circulates through the body in two ways: either bound to other proteins or on its own. PSA traveling alone is called free PSA. The free-PSA test measures the percentage of unbound PSA; the PSA test measures the total of both free and bound PSA. 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 The most promising approach to improve the specificity of PSA, particularly in the range lower 10 ng/ml, is the measurement of molecular isoforms of PSA. These are the disengaged free PSA (fPSA) and the complexed PSA (cPSA) bound to α1-antichymotrypsin. 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. g9mU.