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PSA

Definition

PSA stands for prostate-specific antigen. It is a protein produced by prostate cells.

This article discusses the blood test to measure the amount of PSA in a man's blood. The PSA test is done to help diagnose and follow prostate cancer in men.

Alternative Names

Prostate-specific antigen; Prostate cancer screening test 

How the test is performed

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

How to prepare for the test

Men should not ejaculate for at least 48 hours before the PSA test is done. Doing so may cause a false rise in PSA levels.

Make sure your doctor knows all the medications you're taking. Some drugs may cause your PSA levels to be falsely low. These include finasteride, dutasteride, saw palmetto use, and antiandrogen drugs, such as flutamide, nilutamide, and bicalutamide.

No other special preparation is usually needed.

How the test will feel

When the needle is inserted to draw blood, some people feel moderate pain while others feel only a prick or stinging sensation. Afterward, there may be some throbbing or a bruise.

Why the test is performed

Reasons for a PSA test:

• This test may be done to screen for prostate cancer.
• It is also used to follow patients after prostate cancer treatment to see if the cancer has come back.
• If a healthcare provider feels the prostate gland is not normal during physical exam

For information about prostate cancer screening, see the "Considerations" section below.

Normal Values

No certain PSA level that is called normal or abnormal. No PSA level means you do or do not have prostate cancer. Remember that the PSA test cannot diagnose cancer. Only a biopsy can diagnose cancer. Always discuss PSA test results with your doctor

Your doctor will look at your PSA results and must consider your age, your race, medicines you are taking, and a number of other factors to decide whether your PSA is normal and whether you need more tests done.

Older men typically have slightly higher PSA levels than younger men. Normal ranges by age group commonly used include:

• Men below age 50: PSA less than 2.5
• Men 50 - 59 years: PSA level less than 3.5
• Men 60 - 69 years: PSA level less than 4.5
• Men older than 70 years: PSA level less than 6.5

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What abnormal results mean

A high PSA level has been linked to an increased chance of having prostate cancer. However, a high PSA level only identifies patients at higher risk of having prostate cancer.

As a general guideline, the following results indicate a need for further follow-up and testing:

• A PSA of 4 nanograms per milliliter (ng/mL) for most men
• For men under age 49, levels above 2.5 ng/mL
• For men aged 50 - 59, levels above 3.5 ng/mL
• For men aged 60 - 69, levels above 4.5 ng/mL
• A significant rise from one year to the next may also indicate a higher risk of having prostate cancer.
• African Americans and Asian Americans may need follow-up testing if they have lower PSA levels.
• A rapidly changing PSA, even within the normal range, raises the likelihood of cancer.

Keep in mind that, although PSA testing is an important tool for detecting prostate cancer, it is not foolproof. Your doctor must also think about other factors besides cancer that may cause higher PSA values:

• Men with a larger prostate
• Men who ejaculated in the 48 hours before the blood test was done
• Prostate infection (prostatitis)
• Urinary tract infection
• Recent tests on your bladder (cystoscopy) or prostate (biopsy)
• Catheter tube recently placed into your bladder to drain urine

Your doctor will think about the following factors when deciding on the next step:

• Your age
• If you had a PSA test in the past and how much and how fast your PSA levels have changed
• If your doctor finds a prostate lump during your exam
• Other symptoms you may have
• Other risk factors for prostate cancer, such as race and family history

People at higher risk may need to have more tests. Next steps your doctor may take include:

• Repeating your PSA test, most often sometime within 3 months
• Doing a prostate biopsy so samples of prostate can be viewed under a microscope
• Do a follow-up test called a free PSA (fPSA). The lower the level of this test, the more likely it is that prostate cancer is present.

For someone who has been treated for prostate cancer, the PSA level can show if a treatment is working or if the cancer has come back. Often, PSA levels will begin to rise before there are any symptoms, sometimes months or years beforehand.

What the risks are

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Special considerations

Measuring PSA levels can increase the chance of finding prostate cancer when it is very early.

However, the value of PSA screening for prostate cancer is controversial. There is not a single answer that fits all men. Before having the test, it is best to discuss both the reasons to have and the reasons not to have a PSA test with your doctor.

Some questions you may ask your doctor when discussing having a PSA test include:

• What does an abnormal PSA test mean? Does it mean you have cancer?
• If the PSA test is abnormal, what other tests will be needed? Will you need a biopsy?
• What are your risk factors for prostate cancer? Does that change whether you should have a PSA test? What is the best age to start having a PSA test?
• What are the benefits and risks of finding prostate cancer when it is very early?

If a man chooses to be tested, the PSA is most often done every year to screen:

• Men ages 40 - 75
• Men with a family history of prostate cancer (especially a brother or father) and African-American men, who should think about starting around age 40 - 45. This is because they have a higher chance of developing prostate cancer.

PSA testing is not recommended for screening men over age 75.

There are different recommendations about screening tests for prostate cancer. For more information, check with:

• American Urological Association
• National Comprehensive Cancer Network
• American Cancer Society
• The US Preventive Services Task Force (do not recommend routine PSA testing).

References

American Urological Association. Prostate-specific antigen best practice statement: 2009 update. April 2009. Accessed July 10, 2009.

Lin K, Lipsitz R, Miller T, Janakiraman S; U.S. Preventive Services Task Force. Benefits and harms of prostate-specific antigen screening for prostate cancer: an evidence update for the U.S. Preventive Services Task Force. Ann Intern Med. 2008;149:192-199.

Lim LS, Sherin K; ACPM Prevention Practice Committee. Screening for prostate cancer in U.S. men ACPM position statement on preventive practice. Am J Prev Med. 2008;34:164-170.

Walsh PC, DeWeese TL, Eisenberger MA. Clinical practice. Localized prostate cancer. N Engl J Med. 2007;357:2696-2705.

Walter LC, Bertenthal D, Lindquist K, Konety BR. PSA screening among elderly men with limited life expectancies. JAMA. 2006;296:2336-2342.

Wolf AM, Wender RC, Etzioni RB, Thompson IM, D'Amico AV, Volk RJ, et al. American Cancer Society guideline for the early detection of prostate cancer: update 2010. CA Cancer J Clin. 2010;60:70-98.

Review Date: Sep 23, 2010
Reviewed By: Scott Miller, MD, Urologist in private practice in Atlanta, Georgia. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.