The ratio of free prostate-specific antigen (fPSA) to total prostate-specific antigen (tPSA) is a calculated value used in prostate cancer screening. It is derived by dividing the concentration of fPSA in the blood by the concentration of tPSA. For example, if a patient has an fPSA of 2 ng/mL and a tPSA of 10 ng/mL, the ratio would be 0.2 or 20%. This ratio helps clinicians assess the likelihood of prostate cancer being present.
This value aids in differentiating between benign prostatic hyperplasia (BPH) and prostate cancer, particularly when the tPSA level is within the “gray zone” (typically 4-10 ng/mL). A lower ratio suggests a higher probability of cancer, whereas a higher ratio suggests a higher probability of BPH. Its use can potentially reduce the number of unnecessary prostate biopsies, a procedure with potential complications. The calculation of the ratio emerged as a refinement in prostate cancer screening strategies, aiming to improve specificity and reduce overdiagnosis.
