Anthrax blood test

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The anthrax blood test looks for antibodies against Bacillus anthracis, the bacteria that cause anthrax.

Alternative Names

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

How the Test is Performed

A blood sample is needed.

How to Prepare for the Test

There is no special preparation.

How the Test will Feel

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.

Why the Test is Performed

This test may be performed when the health care provider suspects you have anthrax infection.

Normal Results

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 doctor about the meaning of your specific test results.

What Abnormal Results Mean

An abnormal result means antibodies to B anthracis 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.


There is very 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. 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 lightheaded
  • 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.


Hall GS, Woods GL. Medical bacteriology. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 57.

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. 8th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 209.

Version Info

  • Last reviewed on 9/10/2015
  • Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School; Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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