Histoplasma skin test

Definition
Histoplasma is an infection caused by a fungus that is usually found in the soil. Within the United States, there is a high incidence of infection in certain areas such as the Mississippi, Missouri, and Ohio River Valleys, and in Puerto Rico. The skin test detects exposure to the fungus.

How the test is performed
The test site (an area with hair, usually the forearm) is cleansed. The allergen is then injected just below the skin surface. The test is read at 24 hours and at 48 hours. Occasionally, the reactions may not be present until the 4th day.

How to prepare for the test
No special preparation is necessary for this test.

For infants and children:
The preparation you can provide for this test depends on your child’s age and experience. For specific information regarding how you can prepare your child, see the following topics:

     
  • infant test or procedure preparation (birth to 1 year)  
  • toddler test or procedure preparation (1 to 3 years)  
  • preschooler test or procedure preparation (3 to 6 years)  
  • schoolage test or procedure preparation (6 to 12 years)  
  • adolescent test or procedure preparation (12 to 18 years)

How the test will feel
There will be a brief sting as a needle is inserted just below the skin surface.

Why the test is performed
To see if the individual has been exposed to the fungus that causes histoplasmosis.

Normal Values
No reaction (inflammation) at the site of the test is normal. Of note, the skin test can sometimes make histoplasmosis antibody tests turn positive.

What abnormal results mean
The individual has been exposed to the microorganism that causes histoplasmosis.

What the risks are
There is a slight risk of anaphylactic shock (a severe reaction).

Johns Hopkins patient information

Last revised: December 3, 2012
by Gevorg A. Poghosian, Ph.D.

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