CBC Results for Valley Fever (Coccidioidomycosis)
Typical CBC Findings
The CBC in valley fever is typically normal or shows only nonspecific abnormalities, making it a poor diagnostic tool for this condition. 1 Unlike bacterial infections or tickborne rickettsial diseases where specific patterns emerge, valley fever does not produce characteristic CBC changes that aid in diagnosis.
Expected White Blood Cell Count Patterns
- The total WBC count is usually within normal range in patients with coccidioidomycosis, though mild variations may occur 1
- Leukocytosis (WBC >14,000 cells/mm³) is not a typical feature of valley fever, distinguishing it from acute bacterial infections where this finding has a likelihood ratio of 3.7 for bacterial infection 1, 2
- Left shift (band neutrophils ≥16% or total band count ≥1,500 cells/mm³) is generally absent, unlike bacterial infections where this finding has a likelihood ratio of 14.5 for bacterial infection 1, 2
Other CBC Parameters
- Platelet counts remain normal in valley fever patients, contrasting with tickborne rickettsial diseases where thrombocytopenia occurs in up to 94% of cases 1
- Hemoglobin and hematocrit are typically normal unless chronic disease or disseminated infection develops 1
- Eosinophilia may occasionally be present but is not a consistent or diagnostic finding 1
Clinical Implications for Diagnosis
Valley fever cannot be diagnosed or excluded based on CBC results alone. 1 The diagnosis requires:
- Fungal cultures from respiratory specimens (sputum, bronchoalveolar lavage) to isolate Coccidioides species 1, 3
- Coccidioidal serological testing (complement fixation, immunodiffusion, or enzyme immunoassay) which is the primary diagnostic method 1, 4
- Clinical presentation correlation with epidemiologic factors (residence or travel to endemic areas in southwestern US) 1, 5, 3
Key Diagnostic Pitfall
Do not rely on CBC abnormalities to suggest or exclude valley fever. 1 The most common clinical presentation is a self-limited community-acquired pneumonia that becomes evident 1-3 weeks after infection and is indistinguishable from bacterial or viral infections without specific fungal cultures or serological testing 1. A normal CBC with differential does not rule out coccidioidomycosis, and the absence of leukocytosis or left shift should not delay appropriate diagnostic testing when clinical suspicion exists based on symptoms and epidemiologic exposure 1, 2.