Prostate-specific Antigen (PSA), Free:Total Ratio

In their study, Dr. Catalona and coworkers found that one in four patients with normal DRE and PSA levels between 4.0 and 10.0 ng/mL have prostate cancer ( JAMA. 1998 May 20; 279(19):1542-1547.) They recommend using a cutoff of 25% free PSA for this group of men to identify individuals with an increased risk of prostate cancer. They found that 95% of men with cancer (as determined by biopsy) with normal DRE and total PSA between 4.0 and 10.0 ng/mL had percent free PSA of ≤25%. Their study further indicated that 20% of men with benign disease (as determined by biopsy) with normal DRE and a total PSA between 4.0 and 10.0 ng/mL had percent free PSA greater than the 25% cutoff. The 25% free PSA cutoff detected 95% of cancers while avoiding 20% of unnecessary biopsies.

Alternatively, percent free PSA may be used to determine the relative risk of prostate cancer in individual men. The following table lists the probability of prostate cancer for men with nonsuspicious DRE results and total PSA between 4.0 and 10.0 ng/mL, by patient age.

Note: This test may exhibit interference when a sample is collected from a person who is consuming a supplement with a high dose of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R). It is recommended to ask all patients who may be indicated for this test about biotin supplementation. Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.