Prostate-specific Antigen (PSA), Free:Total Ratio Reflex
PSA circulates through the body in two ways; bound to other proteins or by itself. Unbound PSA is called free PSA. A free-PSA test will measure the percentage of unbound PSA while a PSA test is used to measure the total of free and bound PSA in the blood. The free PSA is a defective variant of normal PSA that can no longer bind to other proteins and so circulates in the blood in the free form. Although the reason why this is the case is poorly understood - patients with prostate cancer may have lower free PSA levels than those with a benign prostate condition.