Leprosy skin test

Alternative names
Lepromin skin test

Definition
The lepromin skin test is used to determine what type of leprosy a person has. It involves the injection of a standardized extract of inactivated leprosy-causing bacteria under the skin.

How the test is performed

An extract sample of inactivated 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 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 needs to have this test performed, it may be helpful to explain how the test will feel, and even practice or demonstrate on a doll. The more familiar your child is with what will happen and why, the less anxiety he or she will feel.

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 a bacteria called Mycobacterium leprae.

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

Normal Values
People who don’t have leprosy will have little or no skin reaction to the antigen. Patients with some forms of leprosy (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.

What the risks are
There is an extremely small risk of an allergic reaction which may include itching and rarely hives.

Special 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.

Johns Hopkins patient information

Last revised: December 4, 2012
by Janet G. Derge, M.D.

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