Mayo Clinic Health Library

PSA test

Updated: 05-07-2013

Definition

The PSA test is used primarily to screen for prostate cancer. A PSA test measures the amount of prostate-specific antigen (PSA) in your blood. PSA is a protein produced in the prostate, a small gland that sits below a man's bladder. PSA is mostly found in semen, which also is produced in the prostate. Small amounts of PSA ordinarily circulate in the blood.

The PSA test can detect high levels of PSA that may indicate the presence of prostate cancer. However, many other conditions, such as an enlarged or inflamed prostate, can also increase PSA levels.

There is a lot of conflicting advice about PSA testing. Ultimately, whether you have a PSA test is something you should decide after discussing it with your doctor, considering your risk factors and weighing your personal preferences.

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Why it's done

Prostate cancer is the most common nonskin cancer in men, and it's the second leading cause of cancer-related death in men after lung cancer. Early detection may be an important tool in getting appropriate and timely treatment.

Men with prostate cancer may have elevated levels of PSA. Many noncancerous conditions also can increase a man's PSA level. Although the PSA test can detect high levels of PSA in the blood, the test doesn't provide precise diagnostic information about the condition of the prostate.

The PSA test is only one tool used to screen for early signs of prostate cancer. Another common screening test, usually done in addition to a PSA test, is a digital rectal exam. In this test, your doctor inserts a lubricated, gloved finger into your rectum to reach the prostate. By feeling or pressing on the prostate, the doctor may be able to judge whether it has abnormal lumps or hard areas.

Neither the PSA test nor the digital rectal exam provides enough information for your doctor to diagnose prostate cancer. Abnormal results in these tests may lead your doctor to recommend a prostate biopsy. During this procedure, samples of tissue are removed for laboratory examination. A diagnosis of cancer is based on the biopsy results.

Other reasons for PSA tests
For men who have already been diagnosed with prostate cancer, the PSA test may be used to:

  • Help decide if and when to begin treatment
  • Judge the effectiveness of a treatment
  • Check for recurring cancer
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What you can expect

A PSA test is done by examining a blood sample in a lab. A nurse or medical technician will use a needle to draw blood from a vein, most likely in your arm.

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Risks

Weighing the benefits, limitations and potential risks of the PSA test can help you make an informed decision.

Benefits of the test
A PSA test may help detect prostate cancer at an early stage.  Cancer is easier to treat and is more likely to be cured if it's diagnosed in its early stages.

But to judge the benefit of the test, it's important to know if early detection and early treatment will improve treatment outcomes and decrease the number of deaths from prostate cancer.

A key issue is the typical course of prostate cancer. Prostate cancer usually progresses slowly over many years. Therefore, a man may have prostate cancer that never causes symptoms or becomes a medical problem during his lifetime.

Limitations of the test
The limitations of PSA testing include:

  • PSA-raising factors. Besides cancer, other conditions that can raise PSA levels include an enlarged prostate (benign prostatic hyperplasia, or BPH) and an inflamed or infected prostate (prostatitis).  Also, PSA levels normally increase with age.
  • PSA-lowering factors. Certain drugs used to treat BPH or urinary conditions may lower PSA levels. Large doses of certain chemotherapy medications can also lower PSA levels.
  • Misleading results. The test doesn't always provide an accurate result. An elevated PSA level doesn't necessarily mean you have cancer. And in some cases, a normal PSA level does not completely rule out prostate cancer.
  • Overdiagnosis. Studies have estimated that between 17 and 50 percent of men with prostate cancer detected by PSA tests have tumors that wouldn't result in symptoms during their lifetimes. These symptom-free tumors are considered overdiagnoses — identification of cancer not likely to cause poor health or to present a risk to the man's life.

Potential risks
The potential risks of the PSA test are essentially related to the choices you make based on the test results, such as the decision to undergo further testing and treatment for prostate cancer. The risks include:

  • Biopsy issues. A biopsy is a procedure that carries its own risks, including pain, bleeding and infection.
  • Psychological effects. False-positive test results — high PSA levels but no cancer found with biopsy — can cause anxiety or distress. If you are diagnosed with prostate cancer, but it appears to be a slow-growing tumor that doesn't result in illness, you may experience significant anxiety just knowing it's there.

Recommendations
A number of major professional organizations and government agencies have weighed in on the benefits and risks of PSA testing. The American Cancer Society, the American Urological Association, the American College of Preventive Medicine, the Centers for Disease Control and Prevention, and the U.S. Preventive Services Task Force all recognize the controversy surrounding screening with the PSA test and the lack of firm evidence that screening can prevent deaths from prostate cancer. Other points of agreement include:

  • Screening needs to be an individualized decision. All of the organizations recommend that doctors discuss the benefits and risks of PSA testing with men at a certain age or in high-risk groups. Doctors should help men make their own decisions about screening, based on age, risk factors, life expectancy and personal preferences.
  • Older men may not need to be screened. Some organizations recommend that screening isn't necessary for men age 75 and older or those who aren't expected to live more than 10 years. The American Cancer Society advises that this decision should be made on an individual basis. It is very important, however, to keep in mind that decisions need to be individualized and not assume that all prostate cancer screening must stop once a man is in his 70s.
  • Men at high risk should discuss screening at an earlier age. Some groups recommend earlier discussions for men in high-risk groups — those with a family history of prostate cancer and African-American men.

The American Cancer Society recommends that doctors provide information about prostate cancer screening to men at average risk starting at age 50, while men at higher risk could benefit from this information at age 40 or 45. The American Urological Association recommends that men consider getting a baseline prostate cancer screening, including a PSA test and DRE, beginning at age 40.

The American Urological Association (AUA) recommends against PSA screening in men under age 40, and it doesn't recommend screening between ages 40 and 54 for men at average risk. For men ages 55 to 69, the AUA recommends shared decision-making between men and their doctors about when to begin screening. The AUA guidelines state that the greatest benefit of screening appears to be in men ages 55 to 69, and it does not recommend routine screening beyond age 70.

The U.S. Preventive Services Task Force (USPSTF) recommends against PSA-based screening for men who do not have symptoms that are highly suspicious for prostate cancer. The USPSTF states that PSA testing in healthy men, regardless of age, offers no net benefit or that the harms outweigh the benefits. This has been a very controversial point of view, and many experts in the field of prostate cancer do not agree with the USPSTF recommendations.

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Results

Results of PSA tests are reported as nanograms of PSA per milliliter of blood (ng/mL). There's no specific cutoff point between a normal and abnormal PSA level. Your doctor might recommend a prostate biopsy based on results of your PSA test and digital rectal exam, along with other factors.

Variations of the PSA test
Your doctor may use other ways of interpreting PSA results before making decisions about ordering a biopsy to test for cancerous tissue. These other methods are intended to improve the accuracy of the PSA test as a screening tool.

Researchers continue to investigate variations of the PSA test to determine whether they provide a measurable benefit. Variations of the PSA test include:

  • PSA velocity. PSA velocity is the change in PSA levels over time. A rapid rise in PSA may indicate the presence of cancer or an aggressive form of cancer.
  • Percentage of free PSA. PSA circulates in the blood in two forms — either attached to certain blood proteins or unattached (free). If you have a high PSA level but a low percentage of free PSA, it may be more likely that you have prostate cancer.  This test is primarily used for men with a PSA level in the borderline range between 4 and 10. It is especially useful when determining the need for re-biopsy rather than in an initial screening state.

Talk to your doctor
Before getting a PSA test, talk to your doctor about the benefits and risks. If you decide that a PSA test is right for you, ask your doctor:

  • When you will discuss the results
  • What kinds of recommendations he or she might make if the results are positive
  • How often you should repeat the test if the results are negative

Discussing these issues beforehand may make it easier for you to learn the results of your test and make appropriate decisions afterward.

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