Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.
Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.
The blood is then tested in a laboratory to look for antibodies. For Brucella, the serum agglutination test (SAT) is the simplest and most widely used testing method.
There is no special preparation.
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.
This test may be performed when the doctor suspects brucellosis.
A normal result shows no antibodies to Brucella. However, during the first few days to weeks of exposure to an antigen, there may be very little antibody production. Therefore, a serology test may not detect early stage disease.
As brucellosis progresses, more antibodies will be present. If the health care provider suspects brucellosis, you may need to have the test repeated 10 days to 2 weeks after the first test to watch for this rise.
Infection with other bacteria, such as Yersinia, Francisella, and Vibrio, and immunizations can make the test falsely positive.
Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
If the test detects antibodies, you have likely been exposed to the Brucella bacteria (possible brucellosis).
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
A serology test can determine if you have ever been exposed to a particular antigen, but this does not necessarily mean that you are currently infected. Increasing antibody levels over a 2-week period are more likely to indicate a current infection.