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.
Prostate-specific antigen; Prostate cancer screening test
How the test is performed
A blood sample is needed. For information on how this is done, see: Venipuncture
How to prepare for the test
Make sure your doctor knows all the medications you are 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.
PSA test results cannot diagnose prostate cancer. Only a prostate biopsy can diagnose this cancer.
Your doctor will look at your PSA results and must consider your age, your race, medicines you are taking, and many other things 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. Commonly used ranges are as follows:
- 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
The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. 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.
In general, the following results need 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. This is called PSA velocity.
- 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.
PSA testing is an important tool for detecting prostate cancer, but it is not foolproof. Other conditions can cause a rise in PSA, including
- A larger prostate
- 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 things 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. Your doctor may recommend:
- Repeating your PSA test, most often sometime within 3 months
- A prostate biopsy
- 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)
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 debated. 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 for you if prostate cancer is found very early?
- What are the risks of not having a PSA test to screen for prostate cancer?
- If prostate cancer is found early, can it be watched without treatment?
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.
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David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc. Louis S. Liou, MD, PhD, Chief of Urology, Cambridge Health Alliance, Visiting Assistant Professor of Surgery, Harvard Medical School.