This blood test looks for antibodies against Francisella tularensis, the bacteria that causes the disease tularemia.

An antibody defends the body against bacteria, viruses, fungus, or other foreign body (antigen). Certain cells tell the body to produce antibodies during an active infection.

In the initial stage of an illness, few antibodies may be detected. Antibody production increases during the course of an infection. For this reason, such tests are often repeated several weeks after the first test is done.

This test specifically looks for the antibodies in the clear liquid portion of the blood, which is called the serum. (This technique is called serology.)

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 blood test may be performed when tularemia is suspected.

No antibodies are detected. However, during the first few days to weeks of exposure to an antigen, 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 several weeks after the first test.

If antibodies are detected, there has been exposure to Franciscella tularensis (possible tularemia).

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 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.