Zero Eosinophil Count on Routine CBC
A zero absolute eosinophil count on routine CBC is generally not concerning in isolation and typically does not require further workup unless accompanied by clinical symptoms, recent corticosteroid use, or other cytopenias. 1
Clinical Significance
Normal eosinophil ranges are 50-500 cells/μL, so a value of zero falls below this threshold but is not inherently pathological. 2, 1
Isolated low eosinophil counts without clinical symptoms generally do not require further investigation. 1 The absence of eosinophils alone does not indicate disease in most clinical contexts.
Corticosteroid therapy is the most common cause of suppressed eosinophil counts, as steroids significantly reduce blood eosinophil levels in most patients. 3, 1 Always verify whether the patient has received systemic or even high-dose inhaled corticosteroids recently.
When to Investigate Further
Consider additional workup only if:
The patient has concurrent cytopenias (low white blood cells, platelets, or hemoglobin), which may suggest bone marrow pathology such as acute myeloid leukemia or myelodysplastic syndromes. 4 These conditions associate more with eosinophil counts approaching zero compared to elevated counts.
There are clinical symptoms suggesting systemic illness, immunodeficiency, or hematologic malignancy. 1
The zero count persists on repeat testing after ruling out corticosteroid exposure or acute illness.
Practical Approach
Verify medication history, particularly any corticosteroid use (oral, inhaled, topical, or intranasal) within the past several weeks. 3, 1
Review the complete CBC for other abnormalities. An isolated zero eosinophil count with otherwise normal CBC parameters requires no action. 1
Repeat the CBC in 4-6 weeks if there is clinical concern or if the patient was recently on steroids, to confirm whether the count normalizes. 5
Eosinophil counts should be interpreted as part of comprehensive clinical assessment rather than in isolation. 1 The American Thoracic Society emphasizes that eosinophil levels are adjunctive markers, not standalone diagnostic criteria.
Common Pitfalls
Do not over-investigate asymptomatic patients with isolated zero eosinophil counts, as this finding alone does not predict disease. 1
Eosinophil counts respond rapidly to corticosteroids, so timing relative to any steroid exposure is critical for interpretation. 3
Avoid confusing low peripheral blood eosinophils with tissue eosinophilia, as peripheral counts may not correlate with tissue inflammation in conditions like eosinophilic esophagitis. 3