A diagnosis of coccidioidomycosis is suspected only if a patient is known to have
had exposure to the disease through travel or residence in an endemic area. Diagnosis
can be confirmed by:
- microscopic identification of the fungal spherules in an infected tissue, sputum
or body fluid sample,
- growing a culture of Coccidioides spp. from a tissue specimen, sputum or body fluid,
- detection of antibodies (serological tests specifically for Valley Fever) against
the fungus in blood serum or other body fluids.
If the serologic test for Valley Fever antibodies is positive, the laboratory then
performs a titer. A titer is a measurement of the amount or concentration of antibodies
a patient is making against the fungus. An antibody is a protein that is produced
in response to an antigen (a substance that causes an immune system response). An
antibody is able to combine with and neutralize the antigen. A titer is obtained
by doubling dilutions of the positive blood (1:4, 1:8, 1:16, 1:32 . . .) until the
test becomes negative. The titer that is reported to your physician is the last
positive dilution. While positive serological results almost always mean that a
patient has Valley Fever, a third or more of patients with Valley Fever may actually
have negative results. Therefore, it may be necessary to repeat the serologic test
Valley Fever skin tests* (called coccidioidin or spherulin) indicate prior exposure
to the fungus, but, because reactivity is lifelong, skin tests are not particularly
helpful in diagnosing a current infection. Commonly, a routine chest x-ray will
detect Valley Fever cavities in a person with no symptoms and who may be unaware
of ever having had Valley Fever.
*The skin test is once again commercially available, as of July 2014.