The coccidiodin skin test checks to see if you are infected with the fungus that causes coccidioidomycosis .
The spherulin test also looks for this fungus, but it may be a more sensitive test. That means it may pick up signs of the infection earlier or more accurately.
Spherulin skin test
How the test is performed:
Coccidiodin and spherulin are substances called antigens that are specifically associated with the fungus that causes coccidioidomycosis.
One of these substances is injected just below the skin's surface, usually in the forearm. Your health care provider will look at your arm 24 hours and 48 hours after the test. If your body has antibodies to the coccidiomycosis fungus, your body will react to the antigen. The area of the shot will become red.
How to prepare for the test:
No special preparation is necessary.
How the test will feel:
There will be a brief sting as a needle is inserted just below the skin's surface.
Why the test is performed:
Doctors once ordered this test if a patient had signs or symptoms of coccidioidomycosis, or had been exposed to the fungus that causes the disease.
However, this skin test is no longer used to diagnosis patients. It is not specific and is mostly used in research to better understand the causes, spread, and control of the disease among a specific group of people.
A normal result means you had no reaction (inflammation) to the antigen contained in the shot.
Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
What abnormal results mean:
An abnormal result (positive result) means you have been exposed to the fungus that causes the disease. However, the exposure may have been in the distant past and may not reflect a current infection. Many people who live in areas where this infection is common may have a positive result but not an active infection.
The test can be positive 2 to 21 days after you develop symptoms. However, many patients do not have a positive reaction even when they have the disease.
False-positives are possible. You may have a positive reaction when you have been exposed to a fungus other than the one that causes coccidiomycosis.
What the risks are:
There is a slight risk of anaphylactic shock (a severe reaction) associated with this skin test.
Chiller TM. Coccidioidomycosis. Infect Dis Clin North Am. 2003;17(1):41-57.
Mandell GL, Bennett JE, Dolin R. Principles and Practice of Infectious Diseases. 5th ed. London, UK: Churchill Livingstone; 2000:2746-2755.
Galgiani JN, Ampel N, Blair JE, et al. Coccidioidomycosis. Clin Infect Dis. 2005;41:1217-1223.