From the Guidelines
Valley Fever labs with low Complement Fixation (CF) titer and positive Immunodiffusion (ID) for IgG antibodies indicate a current or recent infection.
- The presence of IgG antibodies detected by ID test suggests an immune response to the infection 1.
- A low CF titer does not rule out disseminated infection, as patients with extrapulmonary lesions may exhibit variable CF antibody titers 1.
- The diagnosis of disseminated coccidioidomycosis should rely on histopathologic identification or fungal isolation from an extrapulmonary lesion, rather than solely on CF antibody titers 1.
- Treatment with an antifungal agent, such as fluconazole or itraconazole, may be recommended for a duration of 3-6 months, depending on the severity of symptoms and clinical response.
- In severe cases, amphotericin B may be considered for initial therapy, with subsequent step-down to an oral azole antifungal agent.
- It is essential to note that immunosuppressed patients may exhibit significant exceptions to the typical serologic testing results, and their diagnosis and treatment should be approached with caution 1.
From the Research
Interpretation of Valley Fever Labs
The interpretation of Valley Fever labs with low Complement Fixation (CF) titer and positive Immunodiffusion (ID) for IgG antibodies can be understood as follows:
- Low CF titer indicates a low level of complement-fixing antibodies, which are typically associated with the acute phase of coccidioidomycosis 2.
- Positive ID for IgG antibodies suggests the presence of immunoglobulin G antibodies, which are indicative of a past or current infection 3.
Diagnostic Considerations
In the context of Valley Fever diagnosis, the combination of low CF titer and positive ID for IgG antibodies may indicate:
- A past infection with coccidioidomycosis, where the CF titer has decreased over time, but IgG antibodies remain detectable 3.
- A current infection with a low level of complement-fixing antibodies, which may not be detectable by CF testing alone 2.
Limitations of Current Evidence
There is limited direct evidence on the interpretation of Valley Fever labs with low CF titer and positive ID for IgG antibodies. However, studies on coccidioidomycosis diagnosis and treatment provide some insights into the prognostic value of serologic testing, including CF and ID tests 3, 2.