How do you read a free PSA test?

A free PSA test is read in the context of the total PSA test. When the total PSA is between 4 and 10 nanograms per milliliters, the free PSA to total PSA ratio helps to determine the relative risk of prostate cancer, states Mayo Medical Laboratories.

For men with a total PSA level between 4 and 10 nanograms per milliliters, a free to total PSA ratio of 0.1 or less indicates a 49 to 65 percent risk of prostate cancer, depending on age. A free to total PSA ratio of more than 0.25 indicates a 9 to 16 percent risk of prostate cancer, depending on age, explains Mayo Medical Laboratories.