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Blood test
Blood test

PSA
Definition:
This is a test that measures the amount of PSA (prostate-specific antigen) in the blood.

Alternative Names:
Prostate-specific antigen

How the test is performed:

Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (elastic band) or blood pressure cuff is placed around the upper arm to apply pressure, which restricts blood flow through the vein.

This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in air-tight vials or a syringe. During the procedure, the tourniquet is removed to restore circulation.

Once the blood has been collected, the needle is removed, and the puncture site is covered with gauze or a bandage to stop any bleeding.
How to prepare for the test:

No special preparation is usually necessary, but men who engage in sexual intercourse within 24 hours before the PSA test may have a falsely elevated result. Falsely elevated results can also be due to a recent urinary tract infection or a recent surgery on your urinary tract.

You should carefully discuss with your doctor or health care provider whether a PSA test is appropriate for you, because it is not appropriate for all men.
How the test will feel:

When the needle is inserted to draw blood, some people feel moderate pain while others feel only a prick or stinging sensation. Afterward, there may be some throbbing or a bruise.
Why the test is performed:

This test is performed to detect the presence of PSA.

PSA is a glycoprotein (a protein with a sugar attached) found in prostatic epithelial cells. It can be detected at a low level in the blood of all adult men.

The PSA level is greatly increased in most men with prostatic cancer, but can also be increased somewhat in other disorders of the prostate.
Normal Values:

Normal values depend on age. Older men may have slightly higher PSA measurements than younger men. African Americans normally have slightly higher values than white men.

In most laboratories, a value of less than 4 ng/ml is normal. A value between 4 and 10 is borderline, and over 10 is high. Results that are high do not mean that a person has cancer -- other conditions can cause high values. If someone has a high value, further evaluation is neccessary.

Finally, keep in mind that while the PSA test is an important tool for detecting prostate cancer, it is not foolproof. A PSA test does not always detect the presence of cancer. Therefore, a digital rectal exam should also be performed to check for prostate cancer.

Note: ng/ml = nanograms per milliliter

What abnormal results mean:
Greater-than-normal levels may indicate:
What the risks are:
  • fainting or feeling light-headed
  • hematoma (blood accumulating under the skin)
  • infection (a slight risk any time the skin is broken)
  • multiple punctures to locate veins
Special considerations:
The American Urologic Association recommends that all men begin yearly PSA testing at the age of 50. Men with a family history of prostate cancer or men of African decent should consider initiating testing at a younger age.
Review Date: 5/6/2002
Reviewed By: David R. Knowles M.D., Department of Urology, New York-Presbyterian Hospital Columbia Campus, New York, NY. Review provided by VeriMed Healthcare Network.
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