This is an analysis of blood to detect the presence of antibodies against Brucella (the bacteria that causes the disease brucellosis).

Blood is drawn from a vein on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

For an infant or young child, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

The blood is then analyzed in a laboratory. Serology refers to the study of serum (the liquid portion of blood) for its antibody content. Certain microorganisms stimulate the body to produce these antibodies during an active infection. In some cases, the number of antibodies remains high even after the infection clears up. In the laboratory, the antibodies react with antigens in specific ways that can be used to confirm the identity of the specific microorganism.

There are several serology techniques that can be used depending on the suspected antibodies. Serology techniques include agglutination, precipitation, complement-fixation, fluorescent antibodies, and others. For Brucella, the serum agglutination test (SAT) is the simplest and most widely used.

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 brucellosis is suspected.

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. As brucellosis progresses, more antibodies will be present. If brucellosis is suspected, the test may need to be 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.

If antibodies are detected, there has likely been exposure to the Brucella bacteria (possible brucellosis).

The risks associated with having blood drawn are:

• Excessive bleeding
• 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

A serology test can determine if a patient has ever been exposed to a particular antigen, but this does not necessarily indicate a current infection. Increasing antibody levels are more likely to indicate a current infection.

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.