Conditions & Treatments
PSA, or prostate specific antigen, is a protein secreted by normal prostate tissue glands, primarily into the ejaculate fluid, with a small amount measured in the blood. Any inflammatory process, acute injury, benign enlargement, or prostate cancer may elevate the PSA. 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. This screening may improve survival if the tumor is found and treated early.
Factors Affecting PSA Tests
A vigorous digital rectal exam (DRE), such as a prostate massage in evaluating for prostate inflammation, may falsely elevate the PSA. Recent sexual activity or a cytoscopy test may cause PSA levels to rise. The medications finasteride (Proscar) and dutasteride (Avodart), used to treat enlarged prostate, can lower PSA levels by 50 percent. Once a patient starts on 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. Rough handling, contamination, or inadequate refrigeration of the blood sample can cause inaccurate test results.
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.
When preparing for a PSA test, patients should:
- Avoid sexual activity two to three days prior to testing.
- Wait several weeks after having a cytoscopy (a test to evaluate the urethra and bladder).
- Wait until a urinary tract infection or prostatitis has cleared up.
Interpreting Abnormal PSA Results
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. So it is important to obtain a series of PSA values, far enough apart, to demonstrate a significant trend upwards, even within the normal range. For instance, a 52-year-old man with PSA rising from 1.1 to 1.8 to 2.7 over two years would be worrisome, even though his highest PSA is still less than 3.5, the normal for his age group.
Free-PSA is the unbound portion of the total PSA and is more associated with benign disease. So in patients with an elevated total PSA, when the free-PSA fraction is greater than 25 percent, the risk of prostate cancer is low. But if the free-PSA fraction is less than 10 percent, then the risk is high. It is important to remember that free-PSA is really only studied for PSA levels between 4-8 ng/ml.
For most patients, the free-PSA fraction will be between 10 and 24 percent, which is associated with an intermediate risk. The free-PSA is most useful in deciding whether or not to rebiopsy a patient with abnormal PSA following a previous negative biopsy.
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.
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