Understanding a Zero Absolute Eosinophil Count
A zero absolute eosinophil count indicates complete absence of eosinophils in peripheral blood, which can result from bone marrow suppression, severe stress response, or certain medications, and warrants clinical correlation and further investigation to determine the underlying cause. 1
Clinical Significance of Eosinophil Counts
Eosinophils are a type of white blood cell that normally constitute a small percentage of circulating leukocytes. Understanding their absence requires context:
- Normal range: Typically 0.5-5% of white blood cells or 50-500 cells/μL in absolute count 2
- Eosinophilia: Defined as >500 cells/μL
- Hypereosinophilia: Defined as ≥1500 cells/μL 3
- Zero count: Complete absence of circulating eosinophils
Potential Causes of Zero Eosinophil Count
1. Physiologic Causes
- Acute stress response: Endogenous cortisol surge during severe illness, trauma, or surgery
- Diurnal variation: Lowest levels typically occur in the morning due to natural cortisol rhythm
2. Pharmacologic Causes
- Corticosteroid administration: Causes rapid reduction in circulating eosinophils
- Certain chemotherapeutic agents: Can suppress bone marrow production
- Epinephrine: Can cause transient decrease in eosinophil counts
3. Pathologic Causes
- Bone marrow failure: Aplastic anemia or infiltrative processes
- Overwhelming infection: Particularly acute bacterial infections
- Adrenal hyperfunction: Cushing's syndrome
Clinical Approach to Zero Eosinophil Count
Initial Assessment
- Review medication history, particularly recent corticosteroid use
- Evaluate for signs of acute illness or stress
- Review complete blood count for other abnormalities
Further Evaluation
- If isolated finding without explanation:
- Repeat CBC with differential to confirm
- Consider timing of blood draw (morning vs. evening)
- Review patient's clinical status and medication list
When to Be Concerned
- Zero eosinophil count with other cytopenias
- Persistent zero count on repeated measurements
- Associated symptoms suggesting underlying disease
Special Considerations
Technical Factors
- Laboratory-to-laboratory differences can affect measurements
- Time from collection to analysis can impact results 4
- Automated differentials may miss very low levels that manual differentials might detect
Monitoring
- For unexplained zero counts, follow-up testing is recommended
- If associated with medication use, counts typically normalize after discontinuation
- If part of a stress response, counts should recover as the underlying condition improves
Contrast with Eosinophilia
While zero eosinophil count represents one extreme, it's worth noting that elevated counts (eosinophilia) are more commonly encountered clinically and are associated with:
- Allergic disorders
- Parasitic infections
- Certain autoimmune conditions
- Hypereosinophilic syndromes 5
- Eosinophilic esophagitis and other eosinophilic gastrointestinal disorders 5
A zero absolute eosinophil count is not typically seen in allergic or eosinophilic disorders, which are characterized by normal to elevated counts.