How to Order a CBC with Eosinophils
Order a "CBC with differential" (CBC w/diff) - this is the standard test that automatically includes eosinophil counts along with all other white blood cell types.
Ordering Details
When placing your laboratory order, simply request:
- "Complete Blood Count with Differential" or
- "CBC with diff"
This single order provides you with:
- Total white blood cell count
- Percentage of each white blood cell type (including eosinophils)
- Absolute eosinophil count (AEC) - calculated automatically by multiplying the eosinophil percentage by the total WBC count 1
Important Clinical Context
Do not order a CBC without differential if you specifically want eosinophil counts - the basic CBC alone does not include the differential breakdown of white blood cells 2.
Key Points About Eosinophil Interpretation
Once you receive results, focus on the absolute eosinophil count (AEC) rather than just the percentage 1:
- Normal: AEC ≤500 eosinophils/μL
- Eosinophilia: AEC >500 eosinophils/μL
- Hypereosinophilia: AEC ≥1500 eosinophils/μL
This distinction matters clinically because hypereosinophilia (≥1500) is rarely explained by allergy alone and always warrants further workup, whereas mild eosinophilia (500-1500) is commonly secondary to allergies 1.
Common Pitfall to Avoid
Avoid over-ordering CBC w/diff tests. Studies show CBC w/diff is ordered 10-fold more frequently than necessary 2. Order this test only when:
- You suspect a hematologic or infectious disorder
- You need to evaluate for eosinophilia based on clinical suspicion (travel history, allergies, parasitic infection risk)
- Results will actually change your clinical management 3
The CBC w/diff has no value in screening asymptomatic patients from the general population 3.