How the Test is Performed

A sample of inactivated (unable to cause infection) leprosy-causing bacteria is injected just under the skin, usually on the forearm, so that a small lump pushes the skin up. The lump indicates that the antigen has been injected at the correct depth.

The injection site is labeled and examined 3 days, and again 28 days, later to see if there is a reaction.

How to Prepare for the Test

People with dermatitis or other skin irritations should have the test performed on an unaffected part of the body.

If your child is to have this test performed, it may be helpful to explain how the test will feel, and even demonstrate on a doll. Explain the reason for the test. Knowing the "how and why" may reduce the anxiety your child feels.

How the Test Will Feel

When the antigen is injected, there may be a slight stinging or burning sensation. There may also be mild itching at the site of injection afterwards.

Why the Test is Performed

Leprosy is a chronic and potentially disfiguring infection if left untreated. It is caused by Mycobacterium leprae bacteria.

This test is a research tool that helps classify the different types of leprosy. It is not recommended as the main way to diagnosis leprosy.

Normal Results

People who don't have leprosy will have little or no skin reaction to the antigen. Patients with a particular type of leprosy called lepromatous leprosy will also have no skin reaction to the antigen.

What Abnormal Results Mean

A positive skin reaction may be seen in patients with tuberculoid and borderline tuberculoid leprosy. Patients with lepromatous leprosy will not have a positive skin reaction.

Risks

There is an extremely small risk of an allergic reaction which may include itching and, rarely, hives.

Considerations

This test is used primarily as a research tool and only helps in the classification of leprosy. It should not be used to establish a diagnosis of leprosy.

Alternative Names

Leprosy skin test

References

Renault CA, Ernst JD. Mycobacterium leprae. In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2009:chap 251.

Kumar B, Dogra S. The infectious diseases. In: Bope ET, Rakel RE, Kellerman R, eds. Conn's Current Therapy 2011. 1st ed. Philadelphia, Pa: Saunders Elsevier; 2010:section 2.

Updated: 4/24/2012

Reviewed by: Linda Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington School of Medicine; 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. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.