The PSA test is a blood test used primarily to screen for prostate cancer.
The test measures the amount of prostate-specific antigen (PSA) in your blood. PSA is a protein produced by both cancerous and noncancerous tissue in the prostate, a small gland that sits below the bladder in men.
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. Therefore, determining what a high PSA score means can be complicated.
There is a lot of conflicting advice about PSA testing. To decide whether to have a PSA test, discuss the issue with your doctor, considering your risk factors and weighing your personal preferences.
Why it's done
Prostate cancer is common, and a frequent cause of cancer death. Early detection may be an important tool in getting appropriate and timely treatment.
Men with prostate cancer may have elevated levels of PSA. However, many noncancerous conditions also can increase the PSA level. The PSA test can detect high levels of PSA in the blood but 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:
- Judge the effectiveness of a treatment
- Check for recurring cancer
Professional organizations vary in their recommendations about who should — and who shouldn't — get a PSA screening test. Discussing with your doctor 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, and large doses of certain chemotherapy medications, may lower PSA levels. Obesity 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 many men diagnosed with prostate cancer have a normal PSA level.
- Overdiagnosis. Studies have estimated that between 23 and 42 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.
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.
What you can expect
A nurse or medical technician will use a needle to draw blood from a vein, most likely in your arm. The blood sample is then analyzed in the lab to measure your PSA level.
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.
Variations of the PSA test
Your doctor might use other ways of interpreting PSA results before deciding whether to order 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. However, recent studies have cast doubt on the value of PSA velocity in predicting a finding of prostate cancer from biopsy.
- 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.
- PSA density. Prostate cancers can produce more PSA per volume of tissue than benign prostate conditions can. PSA density measurements adjust PSA values for prostate volume. Measuring PSA density generally requires an MRI or transrectal ultrasound.
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.
The Mayo Clinic experience and patient stories
Our patients tell us that the quality of their interactions, our attention to detail and the efficiency of their visits mean health care like they've never experienced. See the stories of satisfied Mayo Clinic patients.