This is a blood test to detect the presence of antibodies against B. anthracis, the bacterium that causes anthrax.

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell 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 infants or young children, 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. A bandage may be applied to the puncture site if there is any bleeding.

The blood is then analyzed in a laboratory. Serology refers to the study of serum for its antibody content. The B. anthracis microorganism stimulates the body to produce antibodies during an active infection. In the laboratory, the antibodies react with antigens in specific ways.

There is no special preparation.

When the needle is inserted to draw blood, you may feel moderate pain, or only a prick or stinging sensation. Afterward, there may be some throbbing.

This test may be performed when anthrax is suspected.

A normal result shows no antibodies present. During the first few days to weeks of exposure to an antigen, however, there may be slight antibody production. As the disease progresses, more antibodies will be present. If a disease is suspected, the test may need to be repeated 10 days - 2 weeks after the first test.

If antibodies are detected, there has been exposure to B. anthracis (possible anthrax). Some people are exposed and do not develop the disease. It is important to see an increase in the antibody titer (count) after a few weeks in order to diagnose a current (rather than a previous) infection. A titer is a measurement of the concentration of a certain substance (in this case, B. anthracis antibody) in a sample.

Treatment with antibiotics can sometimes reduce the antibody response, making titers lower than they would have been without treatment.

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. A person who tests positive for B. anthracis may not develop anthrax.

If repeated tests show markedly increased response, current infection is more likely. In this case, actual symptoms will most likely dictate the best course of therapy before any changes in laboratory test values.

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.