What is Free PSA / Total PSA Ratio?

Free prostate-specific antigen (PSA) tests can help detect signs of prostate cancer. They measure the level of a biomarker that may indicate the condition.
PSA is a substance that the prostate gland produces. Levels vary according to a person’s age and other factors.
Some researchTrusted Source suggests that comparing information about the levels of two types of PSA, free and total PSA, can help confirm a diagnosis of prostate cancer.
This article will examine when a doctor may use a free PSA test, how these differ from total PSA tests, and what the results might mean.

What is a free PSA test?

PSA is a protein that the body produces in the prostate gland and parts of the urinary system. There are different forms of PSA, including total and free PSA. They can either bind to another protein or float freely.
A total PSA test measures all the PSA, including both the bound and the free-floating antigens.
A free PSA test, on the other hand, only measures PSA that is floating freely in the bloodstream and not bound to a different protein.

A doctor can test free and total PSA levels by taking a sample of blood and sending it to a laboratory for analysis. Comparing the two results can help them understand the risk of prostate cancer being present.

Comparing free and total PSA

Comparing the results of total and free PSA tests can give doctors an idea of how likely it is that a person has prostate cancer.
Free PSA ranges can vary, but generally, a higher ratio of free PSA to total PSA indicates a lower risk of prostate cancer. On the other hand, a low ratio of free PSA to total PSA indicates a higher risk of having prostate cancer.

However, PSA tests alone will not confirm a diagnosis, as other factors can affect PSA levels. A digital rectal exam (DRE) and prostate biopsy may also be necessary.

Other factors affecting PSA levels

One reason the result may not be definitive is that other factors can affect PSA levels. These factors include:

• an enlarged prostate gland
• anal sex
• prostate stimulation, such as during a rectal examination
• ejaculation
• medications to treat an enlarged prostate gland
• vigorous exercise
• urinary tract infections
• prostate surgery
• a prostate infection, or prostatitis

A doctor will consider the timing of a PSA test to ensure minimum interaction with other procedures.
For example, a person may need to wait 6 weeks to have a test after:

• bladder or prostate surgery
• the insertion of a catheter
• a prostate biopsy
• a urine infection

Also, a person should not engage in any vigorous exercise for 48 hours before the test.