What are the common causes of eosinopenia?

Common Causes of Eosinopenia

Eosinopenia (low eosinophil count in peripheral blood) is most commonly caused by acute bacterial or viral infections, corticosteroid administration, and stress responses, which should be the first considerations in clinical evaluation.

Definition and Normal Values

• Eosinopenia is defined as an eosinophil count below the lower limit of normal (typically <0.05 × 10⁹/L)
• Normal eosinophil count ranges from 0.05-0.5 × 10⁹/L 1

Major Causes of Eosinopenia

1. Acute Infections

• Bacterial infections - cause marked diminution in circulating eosinophils as part of the host's physiological response 2
• Viral infections - similarly cause eosinopenia during the acute phase 2
• COVID-19 - can cause profound eosinopenia even in patients with pre-existing chronic eosinophilia 3

2. Medication-Induced

• Corticosteroids - most common medication cause through multiple mechanisms:
  • Inhibit eosinophil chemotaxis (dose-dependent and reversible) 4
  • Transiently reduce eosinophil adherence following administration 4
  • Higher doses of dexamethasone can directly inhibit eosinophilopoiesis 5
  • Cause significant reduction in plasma levels of Charcot-Leyden crystal protein 5

3. Stress Response

• Acute stress - triggers endogenous cortisol release leading to eosinopenia
• Critical illness - often associated with eosinopenia, particularly in sepsis
• Surgical stress - post-operative eosinopenia is common

4. Other Causes

• Cushing's syndrome - excess endogenous cortisol production
• Acute myocardial infarction - stress response causes eosinopenia
• Adrenal hyperfunction - increased cortisol production
• Trauma - acute stress response

Clinical Significance

• Eosinopenia during acute infection represents a normal physiological response 2
• In patients with chronic eosinophilia, the development of eosinopenia may signal an acute infection 3
• Persistent eosinopenia in bronchiectasis patients is associated with different clinical outcomes compared to persistent eosinophilia 6
• Eosinophil levels typically return to normal during the remission phase of infection 2

Diagnostic Approach

When evaluating eosinopenia:

1. Review medication history (especially recent corticosteroid use)
2. Assess for signs of acute infection
3. Consider stress-related causes
4. Evaluate for endocrine disorders if persistent
5. Monitor eosinophil count during recovery phase - should normalize as infection resolves 2

Clinical Pearls

• Eosinopenia can be a useful marker for monitoring acute infection - levels typically rise during the remission phase 2
• The precocity and precision with which eosinophil trends follow infection phases make it a reliable parameter for monitoring acute infection 2
• In patients with baseline eosinophilia (e.g., from parasitic infections), development of eosinopenia may indicate a superimposed acute bacterial/viral infection 3
• Eosinopenia in the context of immunosuppressive therapy requires careful monitoring, especially in patients at risk for strongyloidiasis 3

Remember that eosinopenia is often a normal physiological response to acute stress or infection and typically resolves as the underlying condition improves.