Can eosinophil levels be elevated in a Complete Blood Count (CBC) for individuals with allergies?

Eosinophil Levels in CBC Can Be Elevated in Allergic Conditions

Yes, eosinophil levels can be elevated in a Complete Blood Count (CBC) for individuals with allergies, with 10-50% of adults and 20-100% of children with allergic conditions showing elevated peripheral eosinophil counts. 1

Relationship Between Allergies and Eosinophilia

Allergic conditions commonly associated with elevated eosinophil counts include:

• Allergic rhinitis
• Asthma (particularly eosinophilic asthma)
• Atopic dermatitis/eczema
• Food allergies

The elevation in eosinophil counts in allergic conditions is typically modest, usually around 2-fold above normal levels 2. This elevation occurs because allergic responses trigger a Th2-type immune response, which promotes eosinophil production and activation through cytokines like IL-4, IL-5, and IL-13.

Mechanism and Clinical Significance

Eosinophils play several important roles in allergic inflammation:

• They release inflammatory mediators that contribute to tissue damage
• They participate in the allergic cascade through release of cytokines
• They can undergo degranulation, releasing toxic proteins that cause tissue injury

In allergic individuals, eosinophil counts may show seasonal variations, particularly in those with seasonal allergies. This has been documented in conditions like eosinophilic esophagitis, where patients sometimes report seasonal variations in symptoms with corresponding changes in eosinophil levels 2.

Diagnostic Considerations

When interpreting elevated eosinophil counts in CBC:

1. Normal range: Typically <500 cells/μL, though reference ranges may vary between laboratories
2. Mild elevation: Often seen in common allergic conditions
3. Moderate to severe elevation: May indicate more serious conditions like hypereosinophilic syndrome (>1,500 cells/μL)

It's important to note that a normal blood eosinophil count does not exclude tissue eosinophilia, as eosinophils can be present in tissues without significant elevation in peripheral blood 1.

Monitoring and Treatment Implications

Monitoring eosinophil counts can be useful for:

• Assessing response to treatment in allergic conditions
• Following disease activity
• Guiding therapeutic decisions

For example, montelukast (a leukotriene receptor antagonist used in allergic conditions) has been shown to affect eosinophil counts. In patients with seasonal allergic rhinitis aged 15 years and older who received montelukast, a mean increase of only 0.2% in peripheral blood eosinophil counts was noted, compared with a mean increase of 12.5% in placebo-treated patients 3.

Clinical Pearls and Pitfalls

• Pearl: Persistent blood eosinophilia may correlate with persistent symptoms in some allergic conditions 2
• Pitfall: Not all patients with allergies will have elevated eosinophil counts; the absence of eosinophilia does not rule out allergic disease
• Pearl: The degree of elevation in serum eosinophils may correlate with the severity of allergic inflammation in some patients 2
• Pitfall: Elevated eosinophil counts can also be caused by parasitic infections, certain medications, and other inflammatory conditions, so clinical context is essential for proper interpretation

In summary, eosinophilia is a common finding in allergic conditions and can serve as a biomarker for allergic inflammation, though its presence or absence should always be interpreted in the appropriate clinical context.