A blood sample is needed.

There is no special preparation.

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.

This test may be performed when the health care provider suspects you have anthrax infection. The bacteria that cause anthrax is called Bacillus anthracis.

A normal result means no antibodies to the anthrax bacteria were seen in your blood sample. However, during the early stages of infection, your body may only produce a few antibodies, which the blood test may miss. The test may need to be repeated in 10 days to 2 weeks.

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your provider about the meaning of your specific test results.

An abnormal result means antibodies to the bacteria have been detected and you may have anthrax disease. But some people come in contact with the bacteria and do not develop the disease.

To determine if you have a current infection, your provider will look for an increase in the antibody count after a few weeks as well as your symptoms and physical exam findings.

There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood 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 lightheaded
• Multiple punctures to locate veins
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

The best test for diagnosing anthrax is a culture of affected tissue or blood.

Anthrax serology test; Antibody test for anthrax; Serologic test for B. anthracis

Martin GJ, Friedlander AM. Bacillus anthracis (anthrax). In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 207.

Wojewoda CM, Stempak LM. Medical bacteriology. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 57.

Updated by: Jatin M. Vyas, MD, PhD, Associate Professor in Medicine, Harvard Medical School; Associate in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.