Prostate Specific Antigen (cont.)

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What is the free PSA test?

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 found 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.

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 its binding protein. 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 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 doctor 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.

What is PSA velocity and PSA doubling time?

Change in PSA levels over time can be used to assess both cancer risk and aggressiveness of the particular tumor. PSA velocity is defined as an absolute annual increase in serum PSA (ng/mL/year). PSA doubling time is defined as the exponential increase of serum PSA over time and indicates a relative change. These two measures may have a prognostic role in patients that are being treated for prostate cancer. However, studies have shown that using values of these PSA measures for prostate cancer diagnosis do not provide additional information compared to PSA level alone.

Medically Reviewed by a Doctor on 11/3/2015

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