PSA Test (Prostate Specific Antigen)

  • Medical Author: Pamela I. Ellsworth, MD
  • Medical Editor: Melissa Conrad Stöppler, MD
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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What is the cost of the PSA test?

The PSA blood test is frequently covered by insurance, especially for men who are 50 years of age and older. PSA blood tests costs $20-$50. However, if it is obtained in the doctor's office during a visit to the doctor there may be an additional charge of $25-$100 for the office visit. There are PSA blood tests available for home use. The home blood test comes with a lancet to prick your finger and squeeze out a sample of blood, a kit to collect the blood, a bandage, and an address or prepaid mailer to return to the laboratory. Not all of the advertised home blood tests are approved by the U.S. Food and Drug Administration (FDA). You can access the FDA web site to make sure you are using an approved test.

What is the free PSA test?

As described earlier, most of the PSA protein released into the blood becomes attached to other blood proteins. The PSA that does not become attached is known as free PSA and can be measured. It has been observed in small published studies that the level of free PSA is decreased in men who have prostate cancer compared to those with benign conditions. The exact level depends upon which test the laboratory uses, but generally, a test result of less than 10% free PSA is suggestive of cancer. This test is most helpful when the usual PSA test level is between 4.0 ng/mL and 10.0 ng/mL. Nevertheless, free PSA testing has predominantly been used as an adjunct (additional) test along with total PSA, particularly in men who have already undergone a negative prostate biopsy and have a PSA that remains elevated. The ratio of the free/total PSA, as will be discussed in the next section, has helped avoid a second biopsy in many cases.

What is free/total PSA ratio?

Although prostate cancer cells do not produce more PSA than benign prostate tissue, the PSA produced from cancerous cells appears to escape an enzymatic processing that cleaves the bond between PSA and the protein that binds to it. Therefore, men with prostate cancer have a greater fraction of complexed, or bound, serum PSA and a lower percentage of total PSA that is free compared with men without prostate cancer. Therefore, the free/total PSA ratio can be additionally used in clinical practice to discriminate between PSA elevation secondary to benign prostatic disease and prostate cancers. This is particularly useful for patients with a total PSA level between 4.0 and 10.0 ng/mL and a negative normal rectal exam to help the health care provider to decide if a biopsy is necessary. In one study, prostate cancer was found in 56% of men with a free/total PSA less than 0.10 but in only 8% of men with free/total PSA greater than 0.25. Nevertheless, the concept of free PSA must be used with caution as several factors may influence the free/total PSA ratio such as temperature and prostate size. Furthermore, the free PSA measurement is not clinically useful for patients with total serum PSA values less than 10.0 ng/mL or in the follow-up of patients with known prostate cancer.

More recently, a chemical precursor of PSA has been identified, [-2] proenzyme PSA. Preliminary studies show some promise that the level of this chemical, [-2] proenzyme PSA, may help differentiate between prostate cancer and benign enlargement of the prostate (BPH) in men with a normal rectal examination and a PSA between 2.5 and 10 ng/mL.

Medically Reviewed by a Doctor on 2/1/2017

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