Diagnosis and Testing for Valley Fever (Coccidioidomycosis)

How is Valley fever diagnosed?

Healthcare providers rely on your medical and travel history, symptoms, physical examinations, and laboratory tests to diagnose Valley fever. The most common way that healthcare providers test for Valley fever is by taking a blood sample and sending it to a laboratory to look for Coccidioides antibodies or antigens.

Healthcare providers may do imaging tests such as chest x-rays or CT scans of your lungs to look for Valley fever pneumonia(https://www.cdc.gov/pneumonia/). They may also perform a tissue biopsy, in which a small sample of tissue is taken from the body and examined under a microscope. Laboratories may also see if Coccidioides will grow from body fluids or tissues (this is called a culture).

Where can I get tested for Valley fever?

Any healthcare provider can order a test for Valley fever.

How long will it take to get my test results?

It depends on the type of test. Results from a blood test will usually be available in a few days. If your healthcare provider sends a sample to a laboratory to be cultured, the results could take a few days to a couple of weeks.

Skin testing

A skin test can detect whether you have developed an immune response to the fungus Coccidioides, the cause of Valley fever.^1,2 This test became available again in the United States in 2014 for the first time since the late 1990s.² Your healthcare provider might do this test if you have a history of Valley fever.

The test involves getting a small injection on the inside of your forearm, similar to a skin test for tuberculosis. If the test is positive, a bump will appear at the injection site. A healthcare provider must examine the injection site two days (48 hours) after the test was given to measure the size of the bump.

A positive test result means that you have an immune response to Coccidioides because of a past or current Coccidioides infection. Some people with a positive test result have been sick with Valley fever, which can cause a flu-like illness and other symptoms, but many people with a positive test have not had symptoms from the infection. A positive skin test generally means that you are immune to Coccidioides and will not get Valley fever in the future.

A negative skin test can mean that you have not been exposed to Coccidioides and have not had Valley fever. However, some people may not react to the skin test even though they have had a Coccidioides infection. This is called a false-negative result. False-negative results occur more commonly in people who:

• Have had a Coccidioides infection that is recent or severe
• Have a condition or illness that interferes with the skin test results
• Are taking a medication that interferes with the skin test results

For more information about skin testing for Valley fever, talk with your healthcare provider.