The "free" PSA test (PSA-f)
and how it may spare you a biopsy
The free PSA test, often written PSA-f or FPSA, sometimes called
PSA II, helps your urologist decide whether you need a biopsy.
Low free PSA may indicate prostate cancer. High free PSA along with other factors may indicate that you have BPH and no need of biopsy.
The free PSA test measures the proportion of free PSA to bound PSA in the total PSA in your blood sample. It's called this because PSA-f circulates in the bloodstream "unbound," without a carrier protein.
Combined with prostate volume, percent free PSA calculation helps reduce the number of biopsies based on "false positive" PSA test results. This may spare you an unnecessary biopsy.
High free PSA -- above 25% -- usually indicates BPH (benign prostate hyperplasia).
Low free PSA likely signals prostate cancer. Most men with prostate cancer have a free PSA below 15%.
If free PSA is below 7%, prostate cancer is most likely. According to American Cancer Society and National Cancer Institute, men with free PSA at 7% or lower should undergo biopsy. If biopsy is negative but free PSA remains low, repeat biopsy is in order.
If total PSA is low, rate of PSA rise over a series of tests may send a warning. PSA velocity is an independent measure of likely prostate cancer.
Remember, a single PSA test is seldom enough to call for a biopsy. A study published in JAMA (May 28,
2003) says: "An isolated elevation in PSA level should be confirmed several weeks later before proceeding with further testing, including prostate biopsy."
In 2002 a study in Finland found that "Prostate cancer probability depended most strongly on the percentage of free PSA. Total PSA, prostate volume, and DRE also contributed to prostate cancer probability, whereas age and family history of prostate cancer did not." Estimation of prostate cancer risk on the basis of total and free prostate-specific antigen, prostate volume and digital rectal examination. Eur Urol. 2002 Jun;41(6):619-26
The CHART below may help you see the process. The chart is based on information from the American Cancer Society and National Cancer Institute. These charts are not intended as medical advice. Please consult your doctor(s) about prostate cancer and any other prostate and health problems.
For an American Urological Association Chart (March 1, 2000) click here.