Prostate-Specific Antigen (PSA)
A prostate-specific antigen (PSA) test measures the amount of prostate-specific antigen in the blood. PSA is released into a man's blood by his prostate gland. Healthy men have low amounts of PSA in the blood. The amount of PSA in the blood normally increases as a man's prostate enlarges with age. PSA may increase because of inflammation of the prostate gland (prostatitis) or prostate cancer. An injury, a digital rectal exam, or sexual activity (ejaculation) may also briefly raise PSA levels.
Prostate cancer often grows very slowly, without causing major problems. Detecting prostate cancer early and treating it may prevent some health problems and reduce the risk of dying from the cancer. But some treatments for prostate cancer can cause other problems, such as being unable to control urination (incontinence) or erection problems (erectile dysfunction). Some men may choose not to have a PSA test or treat prostate cancer if it is detected. For example, a man older than age 75 who has no bothersome symptoms of prostate cancer may choose not to treat the cancer if it is found, so he would not need a PSA test.
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Why It Is Done
The prostate-specific antigen (PSA) test is done to:
- Screen men for prostate cancer. Experts disagree on the usefulness of PSA testing as a screening tool for prostate cancer. If a PSA test is used for screening, it is usually done for men older than age 50 or for those at high risk for prostate cancer, such as men with a family history of prostate cancer, or for African-American men who have a higher chance of developing cancer than other men. Since other common medical conditions, such as prostatitis, can cause high PSA levels, a prostate biopsy is needed to confirm a diagnosis of cancer.
- Check if cancer may be present when results from other tests, such as a digital rectal exam, are not normal. A PSA test does not diagnose cancer, but it can be used along with other tests to determine if cancer is present.
- Watch prostate cancer and see if treatment is working. If PSA levels increase, the cancer may be growing or spreading. PSA is usually not present in a man who has had his prostate gland removed. A PSA level that rises after prostate removal may mean the cancer has returned or has spread.
How To Prepare
Before you have a prostate-specific antigen (PSA), tell your doctor if you have had a:
- Test to look at your bladder (cystoscopy) in the past several weeks.
- Prostate needle biopsy in the past several weeks.
- Prostate infection (prostatitis) or an urinary tract infection (UTI) that has not gone away.
- Tube (catheter) inserted into your bladder to drain urine recently.
Do not ejaculate during the 2 days before your PSA blood test, either during sex or masturbation.
Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?) .
How It Is Done
The health professional taking a sample of your blood will:
- Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
- Clean the needle site with alcohol.
- Put the needle into the vein. More than one needle stick may be needed.
- Attach a tube to the needle to fill it with blood.
- Remove the band from your arm when enough blood is collected.
- Put a gauze pad or cotton ball over the needle site as the needle is removed.
- Put pressure to the site and then a bandage.
How It Feels
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
There is very little chance of a problem from having a blood sample taken from a vein.
- You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
- In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
- Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.
A prostate-specific antigen (PSA) test measures the amount of prostate-specific antigen in the blood. Normal values may vary from lab to lab.
Because normal PSA levels seem to increase with age, age-specific ranges may be used. But the use of age-specific ranges is controversial, and some doctors prefer to use one range for all ages. For this reason, it is important to discuss your test results with your doctor.
Men age 40–49:
Men age 50–59:
Men age 60–69:
- High levels do not always mean prostate cancer is present. PSA levels may be high if the prostate gland is enlarged (benign prostatic hypertrophy, or BPH) or inflamed (prostatitis).
- PSA levels above 8.0 ng/mL (or 8.0 mcg/L) are likely to mean prostate cancer. A transrectal ultrasound (TRUS) and prostate biopsy are needed to confirm a diagnosis of cancer.
A follow-up test that measures free prostate-specific antigen (free PSA) may be used to see if a prostate biopsy should be done to check for cancer. The lower a man's free PSA level, the more likely he is to develop prostate cancer.
Percent free PSA
Probability of cancer
More than 25%:
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
- Recent sexual activity (ejaculation) or a cystoscopy.
- Recent use of a tube (catheter) to drain urine.
- Recent urinary tract infection (UTI) or prostatitis.
- Large doses of medicines, such as cyclophosphamide (Cytoxan, Neosar), diethylstilbestrol, and methotrexate for cancer treatment.
- The medicine finasteride, such as Proscar or Avodart, which is used to prevent further enlargement of the prostate gland in men with BPH.
What To Think About
- When combined with a digital rectal exam, the prostate-specific antigen (PSA) test increases the chance of detecting prostate cancer. For more information, see the medical test Digital Rectal Examination (DRE).
- A PSA level within the normal ranges does not mean that prostate cancer is not present. Some men with prostate cancer have normal PSA levels.
- The American Cancer Society (ACS) advises doctors about when to
offer the PSA test and DRE:
- Offer these tests to men ages 50 and older who are expected to live more than 10 years.
- Offer these tests to men starting at age 45 if they are at high risk for prostate cancer. This group includes African-American men and men who have a father, brother, or son who was diagnosed with prostate cancer before age 65.
- Offer these tests to men starting at age 40 if they are at an even higher risk for prostate cancer. This group includes men who have several close relatives who had prostate cancer at an early age.
U.S. Preventive Services Task Force (USPSTF) advises
doctors about when to test for prostate cancer:
- No testing is advised for men age 75 and older.
- Before any tests, it is important for men younger than 75 to talk with a doctor about the pros and cons of PSA testing.
- Men younger than 75 who have long-term medical problems or who are expected to live less than 10 years are not likely to benefit from testing.
- Some experts do not advise yearly testing. They say the high rate of false-negative and false-positive results and the costs and risks of further tests outweigh the benefits of yearly screening tests.
- Experts disagree about the type of testing that is appropriate if
the PSA level is high. The decision may depend on:
- Results of your digital rectal exam.
- Results of any PSA tests you have had in the past. If your PSA level gets higher in a short amount of time, follow-up testing may be recommended.
- Your age and health.
- The costs and risks of more tests and treatments.
- Other prostate tests are being evaluated to
determine how well they tell the difference between prostate cancer and benign
- The prostate-specific antigen density (PSAD) test compares the PSA value to the size of the prostate gland. The size of the prostate is measured using transrectal ultrasound (TRUS).
- The PSA velocity test is a measure of how rapidly PSA levels increase over time. PSA levels increase more rapidly in men with prostate cancer and more slowly in men with prostate enlargement (benign prostatic hypertrophy).
- A complexed prostate-specific antigen (cPSA) test may help show if a prostate biopsy should be done. This test measures the amount of a protein made in the prostate (cPSA) that is found in the blood.
Other Works Consulted
- Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
- Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
- Pagana KD, Pagana TJ (2006). Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis: Mosby.
- U.S. Preventive Services Task Force (2008). Screening for Prostate Cancer: Clinical Summary of a U.S. Preventive Services Task Force Recommendation. Also available online: http://www.ahrq.gov/clinic/uspstf/uspsprca.htm.
|Author||Bets Davis, MFA|
|Associate Editor||Pat Truman, MATC|
|Primary Medical Reviewer||Martin Gabica, MD - Family Medicine|
|Specialist Medical Reviewer||Christopher G. Wood, MD, FACS - Urology/Oncology|
|Last Updated||April 13, 2009|