What is the role of skin testing in the workup of coccidioidomycosis?

Updated: Aug 27, 2019
  • Author: Duane R Hospenthal, MD, PhD, FACP, FIDSA, FASTMH; Chief Editor: Michael Stuart Bronze, MD  more...
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Skin testing for diagnosis of coccidioidomycosis involves the intradermal injection of a coccidioidal antigen preparation (eg, coccidioidin, spherulin). The induration of the skin is measured at 24 hours and 48 hours after the injection. An induration greater than 5 mm is considered reactive. Erythema at the injection site does not aid in the diagnosis of coccidioidomycosis. The skin test becomes positive 10-45 days after infection or 2-21 days after symptom onset, preceding the appearance of serologic markers.

Coccidioidin and spherulin are no longer available in the United States. However, Ampel et al found that archived coccidioidin from the 1970s retains its potency and specificity. [58]

The assessment of cutaneous reactivity to coccidioidal antigens has limited diagnostic utility due to low sensitivity and specificity in endemic areas. [4] A dermal delayed-type hypersensitivity reaction to coccidioidin is highly specific for coccidioidal infection. However, a positive result may not be related to current disease because, in most persons, this skin test result remains positive for life after infection. In addition, a low level of cross-reactivity with blastomycosis and histoplasmosis occurs.

Results in infected individuals may be falsely negative because of a lack of immune response. Anergy is common in patients with disseminated disease, even without underlying immunosuppression.

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