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

Antibodies defend the body against bacteria, viruses, fungi, or other foreign substances, calledantigens. Certain cells cause the body to produce antibodies during an active infection.

When you first get sick, few antibodies may be detected. Antibody production increases during the course of an infection. For this reason, antibody tests are often repeated several weeks after the first test is done, so the results can be compared. A rising level of antibodies tells the health care provider that there is indeed an infection.

This test specifically looks for antibodies to F. tularensis in the clear liquid portion of the blood, which is called the serum. (This technique is called serology.) The presence of these particular antibodies indicates a current or previous infection with F. tularensis. In some cases, a single high level of antibodies specific to F. tularensis can indicate infection.

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.

Antibodies are absent. 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.

Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results

If antibodies are detected, there has been exposure to Francisella 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.