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Prostate-Specific Antigen (PSA) Test
A prostate-specific antigen (PSA) test and a digital rectal exam (DRE) are often helpful in diagnosing prostate cancer in men who have no symptoms. PSA is a protein produced by the cells of the prostate gland, a male reproductive gland that makes the fluid that carries sperm during ejaculation. A healthy prostate is a little larger than a walnut. It is located just below the bladder and surrounds the urethra, the tube that allows urine to pass out of the body.
PSA is released along with semen during ejaculation; some PSA makes its way into the bloodstream. A simple blood test is used to measure the level of PSA in the bloodstream.
PSA Test Timetable
For men, the American Cancer Society recommends an annual PSA at:
- Age 40 for men with several close relatives with prostate cancer or cancer at an early age
- Age 45 for men at high risk for all cancers
- Age 50 for all men who do not have major health problems
Check with your primary care physician or urologist to determine a timetable that's right for you and your family history.
Test Results and What They Mean
It is normal for men to have low levels of PSA in their blood. Prostate cancer and benign tumors cause an increase in PSA levels. There is no absolute "normal" PSA level and levels that are considered normal vary between laboratories. The following levels, from the National Cancer Institute at the National Institutes of Health, are often used as a guideline for physicians (measured in nanograms per milliliter (n/mL):
- 0 to 2.5 ng/mL - Low
- 2.6 to 10 ng/mL - Slightly to moderately elevated
- 10 to 19.9 ng/mL - Moderately elevated
- 20 ng/mL or more - Significantly elevated
If PSA levels are abnormal and the digital rectal exam (DRE) is suspicious, a physician will order additional tests, such as a biopsy, ultrasound, and other imaging tests, to determine if cancer is present.
Does an Elevated PSA Level Always Mean Cancer?
Though there is always some risk of the test resulting in a "false negative" (a normal PSA reading when cancer is actually present), an increase in PSA levels may be caused by:
- a prostate gland biopsy
- a resection of the prostate
- rigorous physical activity related to the prostate (i.e. bicycle riding)
- excessive doses of chemotherapeutic drugs
- prostatitis (inflammation of the prostate gland)
- enlarged prostate (benign prostatic hyperplasia - BPA)
- the test returns an elevated PSA level that, after further testing, reveals there is no underlying condition
Treating Increased PSA Levels
A PSA test is a biological marker or sign of an underlying condition. Physicians conduct further tests to determine the cause of the elevated PSA and treat the underlying condition. For example, if the increased PSA level is caused by prostate cancer, physicians treat the cancer.