Blood testing is the most common method used to diagnose Valley Fever. A sample of the pet’s blood is sent to the lab. They look for the presence of antibodies for Valley Fever. If antibodies are present, the lab will then perform a titer test which involves diluting the sample to determine the amount of antibodies which are present. Unfortunately, the titer test is not perfect. It must be interpreted based on other factors. Here’s my general rule for interpreting valley fever titers:
1) No titer – If the lab reports there were no antibodies present it can mean one of three things. a. The pet does not have the disease. b. The pet has the disease but is unable to generate an immune response because it is immunosuppressed. c. The pet hasn’t had the disease long enough to mount an antibody response. That’s why I often recommend rechecking another titer in a few weeks if the pet’s clinical signs fit with Valley Fever.
2) Low titer – People and animals who live in the Sonoran Desert are exposed to the spores all the time. It is common for them to have low titers to Valley Fever. These are referred to as ‘background’ titers. The problem is differentiating a background titer from one that is rising. Again, if the pet’s clinical signs make me suspicious of Valley Fever, I retest these animals at a later date.
3) High titer – A high titer with clinical signs makes the diagnosis easy.
In addition to blood work, X-rays are often helpful in diagnosing Valley Fever. In the lungs, I often seen signs of pneumonia early in the disease. In more chronic cases, circular lesions called granulomas appear. These white lumps are often confused with tumor metastases. Granulomas may appear anywhere in the body. If it is possible to aspirate a granuloma, the diagnosis is made after seeing the organism in the debris.
-Brooks, Wendy. Valley Fever (Coccidioidomycosis), The Pet Health Library, VIN Published 9/26/07 and reviewed in 12/1/09.