What causes eosinopenia?

Causes of Eosinopenia (Zero Eosinophil Count)

Eosinopenia (an eosinophil count of zero) is most commonly caused by acute stress responses, infections, and corticosteroid use, and requires investigation to identify the underlying cause.

Primary Causes of Eosinopenia

1. Acute Stress Response

• Acute stress triggers cortisol release, which causes rapid sequestration of eosinophils from peripheral circulation 1
• Commonly seen in:
  • Acute myocardial infarction (associated with worse clinical outcomes) 2
  • Trauma
  • Surgery
  • Severe physical or emotional stress

2. Infections

• Acute bacterial infections (particularly sepsis)
• Viral infections during acute phase
• Mechanism: Endogenous corticosteroid release and inflammatory cytokines cause eosinophil margination

3. Medication-Induced

• Corticosteroids: Most common drug cause - both endogenous and exogenous steroids rapidly reduce circulating eosinophils 1
• Other medications:
  • Some chemotherapeutic agents
  • Certain antibiotics
  • NSAIDs (in some cases)

4. Adrenal Hyperfunction

• Cushing's syndrome
• Adrenal tumors producing excess cortisol

Less Common Causes

5. Acute Phase of Certain Diseases

• Early stages of urticaria (before eosinophilia develops) 3
• Some autoimmune conditions during flares

6. Bone Marrow Disorders

• Aplastic anemia
• Myelofibrosis
• Some leukemias that suppress normal bone marrow function

Clinical Significance

• Eosinopenia in acute myocardial infarction correlates with larger infarct size and worse clinical outcomes (28.8% vs 20.4% adverse events) 2
• In chronic spontaneous urticaria, eosinopenia is associated with:
  • Higher disease activity
  • Autoimmunity markers
  • Poor response to antihistamines and omalizumab 3
• Can serve as an inflammatory marker in critical illness

Diagnostic Approach

1. Confirm true eosinopenia:

   • Repeat CBC with differential to verify zero eosinophil count
   • Review peripheral blood smear

2. Assess for acute stress or infection:

   • Check vital signs, inflammatory markers (CRP, procalcitonin)
   • Blood cultures if infection suspected

3. Medication review:

   • Focus on recent or current corticosteroid use
   • Review all medications for potential causes

4. Evaluate for underlying conditions:

   • Cortisol levels if adrenal dysfunction suspected
   • Consider bone marrow evaluation if other cytopenias present

When to Be Concerned

• Persistent eosinopenia without obvious cause
• Eosinopenia with other cytopenias (may indicate bone marrow disorder)
• Eosinopenia in the setting of acute myocardial infarction (indicates worse prognosis) 2

Management

• Treatment is directed at the underlying cause
• Eosinopenia itself typically resolves when the underlying condition is addressed
• Monitor eosinophil counts during recovery phase to ensure normalization

Remember that while eosinophilia (elevated eosinophils) often receives more clinical attention, eosinopenia can be an important diagnostic clue and prognostic indicator in various clinical scenarios.