Prostate-Specific Antigen (PSA) Blood Test

Prostate-specific antigen (PSA) is a substance produced by the prostate gland. Elevated PSA levels may indicate prostate cancer, a noncancerous condition such as prostatitis, or an enlarged prostate.

Most men have PSA levels under four (ng/mL) and this has traditionally been used as the cutoff for concern about the risk of prostate cancer. Men with prostate cancer often have PSA levels higher than four, although cancer is a possibility at any PSA level. According to published reports, men who have a prostate gland that feels normal on examination and a PSA less than four have a 15% chance of having prostate cancer. Those with a PSA between four and 10 have a 25% chance of having prostate cancer and if the PSA is higher than 10, the risk increases and can be as high as 67%.

In the past, most experts viewed PSA levels less than 4 ng/mL as normal. Due to the findings from more recent studies, some recommend lowering the cutoff levels that determine if a PSA value is normal or elevated. Some researchers encourage using less than 2.5 or 3 ng/mL as a cutoff for normal values, particularly in younger patients. Younger patients tend to have smaller prostates and lower PSA values, so any elevation of the PSA in younger men above 2.5 ng/mL is a cause for concern.

Just as important as the PSA number is the trend of that number (whether it is going up, how quickly, and over what period of time). It is important to understand that the PSA test is not perfect. Most men with elevated PSA levels have noncancerous prostate enlargement, which is a normal part of aging. Conversely, low levels of PSA in the bloodstream do not rule out the possibility of prostate cancer. However, most cases of early prostate cancer are found by a PSA blood test.

How Is The PSA Screening Test Done?

The test involves drawing blood, usually from the arm. The results are usually sent to a lab and most often come back within several days.

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When Should I Have My PSA Levels Tested?

The American Cancer Society says men should talk to their doctors about the benefits, risks, and limitations of prostate cancer screening before deciding whether to be tested. The group's guidelines make it clear that prostate-specific antigen (PSA) blood testing should not occur unless this discussion happens. They recommend that most men at average risk for prostate cancer start the discussion at age 50 and those with higher risk for prostate cancer should start the discussion earlier.

The American Urological Association recommends that men ages 55 to 69 who are considering screening should talk with their doctors about the risks and benefits of testing and proceed based on their personal values and preferences. The group also adds:

  • PSA screening in men under age 40 is not recommended.
  • Routine screening in men between ages 40 and 54 at average risk is not recommended.
  • To reduce the harms of screening, a routine screening interval of two years or more may be preferred over annual screening in those men who have decided on screening after a discussion with their doctor. As compared to annual screening, it is expected that screening intervals of two years preserve the majority of the benefits and reduce over diagnosis and false positives.
  • Routine PSA screening is not recommended in men over age 70 or any man with less than a 10-15 year life expectancy.

The U.S. Preventive Services Task Force, however, doesn't recommend routine PSA screening for men in the general population, regardless of age. They say the tests may find cancers that are so slow-growing that medical treatments -- which can have serious side effects -- would offer no benefit.

If your doctor is concerned that you might have prostate cancer based on either a PSA level or a rectal exam, a biopsy (a lab testing of a small amount of tissue from the prostate) will be the next step. This is the only way to positively identify the presence of cancer.

What Does an Elevated PSA Level Mean?

Elevated PSA levels may indicate prostate cancer or a noncancerous condition such as prostatitis or an enlarged prostate.

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Your PSA level can also be affected by other factors:

If your PSA level is high, your doctor may recommend that you get a prostate biopsy to test for cancer.

Alternative PSA Testing

There are some new PSA tests that may help you and your health care provider determine if you need a biopsy. You should know that doctors do not always agree on how to use or analyze the results of these additional tests.

  • Percent-free PSA. PSA takes two major forms in the blood. One is attached, or bound, to blood proteins and the other circulates freely. The percent-free PSA test indicates how much PSA circulates free compared to the total PSA level. The percentage of free PSA is lower in men who have prostate cancer than in men who do not. Studies show that if your PSA results are in the borderline range (4 to 10), a low percent-free PSA (less than 10%) means that the likelihood of having prostate cancer is about 50% and that you should probably have a biopsy.

    Some doctors recommend biopsies for men whose percent-free PSA is 20 or less.

  • PSA velocity. The PSA velocity is not a separate test. Rather, it is the change in PSA levels over time. Even when the total PSA value isn't higher than 4, a high PSA velocity (an increase greater than 0.75 ng/mL in one year) suggests that cancer may be present and a biopsy should be considered.
  • Urine PCA3 test. This urine test looks for a fusion of genes that is present in 50% of PSA-tested men with prostate cancer. It's another tool to determine if a man may need a biopsy.

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Using the PSA Blood Test After Prostate Cancer Diagnosis

Although the PSA test is used mainly to screen for prostate cancer, it is valuable in other situations:

  • To guide treatment. Along with a doctor's exam and tumor stage, the PSA test can help determine how advanced a prostate cancer is. This may affect treatment options.
  • To determine treatment success. After surgery or radiation, the PSA level can be monitored to help determine if treatment was successful. PSA levels normally fall to very low levels if the treatment removed or destroyed all of the cancer cells. A rising PSA level can mean that prostate cancer cells are present and your cancer has come back.

If you choose a "watchful waiting" approach to treatment, the PSA level can help determine if the disease is progressing and if active treatment should be considered.

During hormonal therapy, the PSA level can help indicate how well the treatment is working or when it may be time to try another treatment.

WebMD Medical Reference Reviewed by Minesh Khatri, MD on October 20, 2016

Sources

SOURCES: 

New England Journal Of Medicine.

American Urological Association. 

National Cancer Institute. 

American Cancer Society. 

News release, U.S. Preventive Services Task Force.

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