Alternative Names prostatic-specific antigen density, PSAD
Definition This test measures the size of the prostate gland and relates it to the level of a special protein in the blood. The protein is called prostate-specific antigen (PSA). This test is used to identify men who are more likely to have prostate cancer. The PSA density test may be better at this than the standard PSA test. However, many experts think PSA density values are misleading. They do not use this test to check for prostate cancer.
Who is a candidate for the test? Men with a slightly high standard PSA test value, who have a normal rectal examination, are possible candidates for this test.
How is the test performed? A blood sample is obtained first. This usually involves inserting a fine needle into a vein in the forearm or hand to draw blood. The blood sample is sent to the laboratory to measure the PSA level.
The size of the prostate is then measured by transrectal ultrasound. This test bounces sound waves off of the prostate gland using a rectal probe. The probe is a slender, flexible surgical instrument with a blunt bulb-type tip. It is used to explore the rectum. The PSA density test value is calculated by dividing the standard blood PSA level by the size of the prostate.
What is involved in preparation for the test? A cleansing enema is recommended either the night before or the morning of the test. During an enema, liquid is injected into the rectum through the anus. This cleans the bowels in preparation for the test.
What do the test results mean? Normally, a man with a large prostate gland will have a higher PSA density value than men with a smaller prostate gland, assuming neither has cancer of the prostate. The standard PSA value is often proportional to the size of the prostate gland. Men with standard PSA values that are out of proportion with the size of their prostate gland might have prostate cancer. On the other hand, a man with a very large prostate and a slightly increased standard PSA value might not have prostate cancer. A PSA density value or score of greater than roughly 0.15 suggests prostate cancer may be present. Men with PSA density scores above this number should consider additional tests. These include a prostate gland biopsy. A biopsy is a procedure to remove a small piece of tissue. The tissue can then be sent to a laboratory to see if it contains cancer. PSA values are dependent on a number of factors. Your doctor will advise you accordingly or refer you to a urologist if he/she has any doubt.
Author: Gary Kearney, MD Reviewer: eknowhow Medical Review Panel Editor: Dr John Hearne Last Updated: 6/06/2005 Contributors Potential conflict of interest information for reviewers available on request
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