PSA, or prostate-specific antigen, is a protein secreted by normal prostate glands that allow normal sperm function and be measured in the blood. It is often used as a screening tool for prostate cancer, but levels can be elevated from infection, inflammation, trauma, or benign enlargement.
A variety of conditions lead to elevation of PSA, including inflammation, acute injury, benign enlargement, or prostate cancer. This blood test is used to identify men who are at high risk for prostate cancer and may benefit from more diagnostic tests to look for prostate cancer.
After discussion of the risks and benefits of cancer screening, most primary care physicians usually draw the PSA with routine blood tests at the time of annual physical examinations, starting at age 50 for most men or at age 40 for patients at higher risk. Higher risk patients include men with a family history of prostate cancer or African Americans. Screening may improve survival if the tumor is found and treated early.
Factors Affecting PSA Tests
Several activities can impact the results of a PSA test. Straddle activities like long-distance bicycle riding, recent sexual activity, a vigorous digital rectal exam (DRE), or a cystoscopy test may cause PSA levels to be temporarily elevated and should be avoided for at least 48 hours before the blood draw.
The medications finasteride (Proscar) and dutasteride (Avodart), used to treat enlarged prostate, can lower PSA levels by 50 percent. Once a patient starts one of these medications, a PSA should be drawn to establish a new baseline. Whenever future PSAs are done, this new baseline should be used for reference.
In men older than 75, PSA testing is controversial. This stems from the fact that these older men have a high likelihood of slow-growing prostate cancer while also having medical problems like heart disease, diabetes, neurologic conditions, and other cancers. In addition, PSA screening is not recommended in any patient with major medical problems and a life expectancy of less than 10 years, as these patients would be more likely to die with prostate cancer rather than from prostate cancer.
When preparing for a PSA test, patients should:
- Avoid sexual activity two to three days prior to testing.
- Wait several weeks after having a cystoscopy (a test to evaluate the urethra and bladder).
- Wait until symptoms of urinary tract infection or prostatitis have resolved.
Interpreting Abnormal PSA Results
PSA should always be interpreted relative to previous PSA tests, patient age and the size of the prostate. The PSA slope refers to the change in PSA over a sustained period of time: years rather than months. While an individual abnormal PSA may prompt concern, many of these situations are temporary elevations from benign conditions, and the PSA will later return to normal. But when the PSA level steadily rises with significant jumps over a period of time, then there is greater likelihood of prostate cancer. Additionally, PSA normal levels different by age, with higher normal levels in older patients.
Regarding prostate size, since PSA is also made by normal prostate tissue (not cancer) it is possible that a very large prostate will generate a large (but still normal) amount of PSA. Size of the prostate should be determined by imaging rather than simple physical exam, and it is important to remember that having an enlarged prostate does not prevent the development of prostate cancer.
A digital rectal examination (DRE) is still a key part of an annual physical exam, even in the PSA era. A prostate nodule or an irregular-feeling prostate may indicate an early prostate cancer despite a normal PSA test.