Eosinophils (EO#)

Immune cells involved in allergic reactions and parasite defence.

What it is

Eosinophils are white blood cells specialised for fighting parasites and participating in allergic and inflammatory responses. They make up a small fraction of circulating immune cells.

Why it matters

Elevated eosinophils during cancer treatment can signal a drug hypersensitivity reaction. Significant eosinophilia (>1.5 ×10⁹/L) may indicate a rare condition called hypereosinophilic syndrome. Most often, mild elevation reflects allergy or resolved infection.

How to test

Full blood count differential.

This information is for educational purposes only. Always discuss testing and interpretation of results with your care team.

Optimal range

0.02–0.5 ×10⁹/L.

How often

Each blood count panel.