David Baxter PhD
Late Founder
PSA test
By Mayo Clinic staff
May 13, 2009
The PSA test is used primarily to screen for prostate cancer before symptoms appear. 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 about the size and shape of a walnut that sits below a man's bladder. Small amounts of PSA ordinarily circulate in the blood.
The prostate produces and releases a component of semen, the fluid that transports sperm during ejaculation. Some problems with the prostate, such as an enlarged prostate and prostate cancer, become more likely as men age.
Use of the PSA test is controversial. It's important to discuss with your doctor whether you should get a PSA test and what the results may mean.
Why it's done
Prostate cancer is the second most common cancer in men after skin cancer. Early detection may be an important tool in getting appropriate and timely treatment.
Cancerous (malignant) tissue of the prostate usually produces more PSA than healthy tissue. The PSA test can detect high levels of PSA that may indicate the presence of prostate cancer. However, other conditions, like an enlarged or inflamed prostate, may also increase PSA levels. Therefore, 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 in order to reach the prostate. By feeling or pressing on the prostate, your doctor may be able to judge whether it's enlarged or has abnormal lumps.
Neither the PSA test nor the digital rectal exam provides enough information for your doctor to make a diagnosis of prostate cancer. Abnormal results in these tests, however, may lead your doctor to order a prostate biopsy, a procedure that removes samples of tissue for laboratory examination. A diagnosis of prostate cancer is based on the results of a biopsy.
Other reasons for PSA tests
For men who have already been diagnosed with prostate cancer, the PSA test may be used to:
A PSA test is done by an examination of a blood sample. A nurse or medical technician will use a needle to draw blood from a vein, most likely a vein in your arm. The site on your arm may be tender for a few hours, but you'll be able to resume most normal activities after the sample is taken.
Risks
The risks associated with a PSA test are related to what's done in response to the information you get from the test. In other words, will the benefit of knowing the results of a PSA test outweigh the potential risk of knowing?
Expected benefit
It seems that any test indicating whether you may have cancer would be beneficial. Indeed, a PSA test can often detect prostate cancer at an early stage.
But to judge the benefit of the PSA test, you need to know the answer to the following question: Do early detection and early treatment improve treatment outcomes and decrease the number of deaths from prostate cancer? Two recent large studies have produced somewhat competing answers, leading many experts to argue that there isn't enough evidence to answer this question.
A key issue is the typical course of prostate cancer. If all cases of prostate cancer progressed rapidly and caused poor health and death, then early detection would clearly be a good thing. However, prostate cancer usually progresses slowly over many years, and the majority of cases are diagnosed in men over the age of 65. Therefore, a man may have prostate cancer that never causes symptoms or never becomes a medical problem.
Limitations of the test
The limitations of the PSA test make it difficult to judge the benefit and risk of getting the test. These limitations include:
The potential risks of the PSA test are related to results of the test and the choices you make based on those results. All of the variables related to prostate cancer and PSA test results contribute to the following risks:
A number of organizations have published guidelines for PSA testing. Recommendations by professional organizations and government agencies include the following:
Results of PSA tests are reported as nanograms of PSA per milliliter of blood (ng/mL). A PSA result of 4.0 ng/mL has generally been considered the cut-off point. Therefore, if you have a PSA of 4.0 or higher, your doctor may recommend a biopsy to determine if there's any cancerous tissue.
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.
There's little clinical evidence ? as with standard PSA tests ? that these variations on the PSA screening test improve treatment outcomes or decrease the number of deaths. Researchers continue investigating these strategies to determine if they provide a measurable benefit. Variations of the PSA test include:
By Mayo Clinic staff
May 13, 2009
The PSA test is used primarily to screen for prostate cancer before symptoms appear. 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 about the size and shape of a walnut that sits below a man's bladder. Small amounts of PSA ordinarily circulate in the blood.
The prostate produces and releases a component of semen, the fluid that transports sperm during ejaculation. Some problems with the prostate, such as an enlarged prostate and prostate cancer, become more likely as men age.
Use of the PSA test is controversial. It's important to discuss with your doctor whether you should get a PSA test and what the results may mean.
Why it's done
Prostate cancer is the second most common cancer in men after skin cancer. Early detection may be an important tool in getting appropriate and timely treatment.
Cancerous (malignant) tissue of the prostate usually produces more PSA than healthy tissue. The PSA test can detect high levels of PSA that may indicate the presence of prostate cancer. However, other conditions, like an enlarged or inflamed prostate, may also increase PSA levels. Therefore, 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 in order to reach the prostate. By feeling or pressing on the prostate, your doctor may be able to judge whether it's enlarged or has abnormal lumps.
Neither the PSA test nor the digital rectal exam provides enough information for your doctor to make a diagnosis of prostate cancer. Abnormal results in these tests, however, may lead your doctor to order a prostate biopsy, a procedure that removes samples of tissue for laboratory examination. A diagnosis of prostate cancer is based on the results of a biopsy.
Other reasons for PSA tests
For men who have already been diagnosed with prostate cancer, the PSA test may be used to:
- Monitor possible changes in the tumor
- Judge the effectiveness of a treatment
- Check for recurring cancer
A PSA test is done by an examination of a blood sample. A nurse or medical technician will use a needle to draw blood from a vein, most likely a vein in your arm. The site on your arm may be tender for a few hours, but you'll be able to resume most normal activities after the sample is taken.
Risks
The risks associated with a PSA test are related to what's done in response to the information you get from the test. In other words, will the benefit of knowing the results of a PSA test outweigh the potential risk of knowing?
Expected benefit
It seems that any test indicating whether you may have cancer would be beneficial. Indeed, a PSA test can often detect prostate cancer at an early stage.
But to judge the benefit of the PSA test, you need to know the answer to the following question: Do early detection and early treatment improve treatment outcomes and decrease the number of deaths from prostate cancer? Two recent large studies have produced somewhat competing answers, leading many experts to argue that there isn't enough evidence to answer this question.
A key issue is the typical course of prostate cancer. If all cases of prostate cancer progressed rapidly and caused poor health and death, then early detection would clearly be a good thing. However, prostate cancer usually progresses slowly over many years, and the majority of cases are diagnosed in men over the age of 65. Therefore, a man may have prostate cancer that never causes symptoms or never becomes a medical problem.
Limitations of the test
The limitations of the PSA test make it difficult to judge the benefit and risk of getting the test. These limitations include:
- PSA-raising factors. 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. Men who are obese tend to have lower PSA levels. Medications to treat BPH and some dietary supplements taken for prostate health can lower PSA levels. These factors, therefore, may mask the presence of cancer.
- False-positives. Getting a positive result on a PSA test ? a PSA level high enough to suggest you may have cancer ? doesn't mean you have cancer. About 75 percent of men who get a biopsy after a positive PSA test don't have cancer. These test results are called false-positives.
- False-negatives. Getting a negative result on a PSA test doesn't prove that you don't have cancer. Some men with negative results ? low levels of PSA suggesting no cancer ? will later be diagnosed with prostate cancer. If a test misses the presence of cancer, the result is called a false-negative.
- Overdiagnosis. Studies have estimated that between 29 and 44 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 person's life.
The potential risks of the PSA test are related to results of the test and the choices you make based on those results. All of the variables related to prostate cancer and PSA test results contribute to the following risks:
- Treatment side effects. Possible side effects of treatments for prostate cancer include an inability to get or maintain an erection (erectile dysfunction), inability to control urine flow (urinary incontinence), problems with bowel movements, and death. These risks may seem acceptable if you know untreated disease would cause severe illness or death. But it's difficult to decide whether these risks are worth taking ? whether the treatment does more harm than good ? if prostate cancer is detected very early, when its future course is often unknown.
- Biopsy issues. A biopsy is an expensive, invasive procedure that has its own risks, including pain.
- Psychological effects. False-positive test results ? high PSA levels but no cancer found with biopsy ? can produce a significant amount of anxiety or distress. You may worry about whether the PSA test or the biopsy was correct. 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 anxiety just knowing it's there.
A number of organizations have published guidelines for PSA testing. Recommendations by professional organizations and government agencies include the following:
- The U.S. Preventive Services Task Force concludes that the current evidence is insufficient to assess the benefits and risks of PSA testing to screen for prostate cancer in men younger than 75. It also recommends that screening shouldn't be done with men age 75 and older. The Centers for Disease Control and Prevention (CDC) and other U.S. government agencies follow these guidelines.
- The American College of Preventive Medicine recommends that for men age 50 or older who are expected to live at least 10 years, doctors provide information about the benefits and risks of screening and the limits of current evidence about the value of early testing and treatment. The organization also recommends that doctors help men make their own choices about screening.
- The American Cancer Society doesn't support routine PSA tests for prostate cancer. It does recommend that doctors discuss the benefits and risks of PSA testing with men who are age 50 and expected to live at least 10 years. It recommends earlier discussions for men in high-risk groups ? men with a family history of prostate cancer and African-American men.
- The American Urological Association believes that doctors should offer a baseline PSA test to men at age 40. How often the PSA test should be repeated depends on the results of the baseline PSA test. The association also recommends that doctors discuss the benefits and risks with their patients.
Results of PSA tests are reported as nanograms of PSA per milliliter of blood (ng/mL). A PSA result of 4.0 ng/mL has generally been considered the cut-off point. Therefore, if you have a PSA of 4.0 or higher, your doctor may recommend a biopsy to determine if there's any cancerous tissue.
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.
There's little clinical evidence ? as with standard PSA tests ? that these variations on the PSA screening test improve treatment outcomes or decrease the number of deaths. Researchers continue investigating these strategies to determine if 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.
- Age-adjusted PSA. Age-adjusted PSA is an adjustment of the cut-off point for recommending a biopsy. Because PSA levels increase with age, it may be appropriate to lower the cut-off for younger men and raise it for older men.
- 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.
- Screening for prostate cancer: U.S. Preventive Services Task Force recommendation statement. Annals of Internal Medicine. 2008;149:185.
- Overview: Prostate cancer. How many men get prostate cancer? American Cancer Society. ACS :: How Many Men Get Prostate Cancer?
- The prostate-specific antigen (PSA) test: Questions and answers. National Cancer Institute. Prostate-Specific Antigen (PSA) Test - National Cancer Institute
- What You Need to Know About Prostate Cancer. Rockville, Md.: National Cancer Institute; 2008.
- Can prostate cancer be found early? American Cancer Society. ACS :: Can Prostate Cancer Be Found Early?
- Lin K, et al. Benefits and harms of prostate-specific antigen screening for prostate cancer: An evidence update for the U.S. Preventive Services Task Force. Annals of Internal Medicine. 2008;149:192.
- Prostate cancer: Screening. Centers for Disease Control and Prevention. CDC - Prostate Cancer Screening
- Ferrini R, et al. Screening for prostate cancer in American men: American College of Preventive Medicine Practice Policy Statement. American College of Preventive Medicine. Screening for Prostate Cancer
- Early detection of prostate cancer. American Urological Association. AUA - Policy Statements
- Andriole GL, et al. Mortality results from a randomized prostate-cancer screening trial. New England Journal of Medicine. 2009;360:1310.
- Schroder FH, et al. Screening and prostate-cancer mortality in a randomized European study. New England Journal of Medicine. 2009;360:1320.
- Carroll P, et al. Prostate-specific antigen best practice statement: 2009 update. American Urological Association. http://www.auanet.org/content/guidelines-and-quality-care/clinical-guidelines/main-reports/psa09.pdf
