7 Eosinophils.

Eosinophils — allergy, parasites, drug reactions; grades of eosinophilia and hypereosinophilia and organ risks.

Eosinophils are white blood cells with large orange-red granules. Their granules contain toxic proteins that damage parasites, and they take part in allergic inflammation. Eosinophils live mainly in tissues (the gut, lungs and skin), and only a small number circulate in the blood. An increased count, eosinophilia, is most often caused by allergy or parasites, but it can also reflect drug reactions, autoimmune diseases or rare blood disorders.

Complete blood countWhite cell differentialAllergy

Share of white cellsabout 1–4 %

Absolute count0.03–0.35 ×10⁹/L

Eosinophilia> 0.5 ×10⁹/L

Hypereosinophilia> 1.5 ×10⁹/L

Figure 1. Eosinophils normally make up only a few percent of circulating white cells; their count changes quickly with allergies, infections and hormones.

Grades of eosinophilia

Thresholds according to the international consensus on eosinophilic disorders (Valent et al., 2012).
Absolute count	Grade
0.5–1.5 ×10⁹/L	eosinophilia
> 1.5 ×10⁹/L (on two tests at least a month apart)	hypereosinophilia

Causes of eosinophilia

Allergic diseases: asthma, allergic rhinitis, atopic dermatitis, eosinophilic oesophagitis
Parasites: worms (roundworm, hookworm, Strongyloides, Toxocara, schistosomes) — especially after travel or in areas with poor sanitation
Drug reactions: antibiotics, anticonvulsants, allopurinol; DRESS syndrome is a severe reaction with rash, fever and organ involvement
Autoimmune and inflammatory diseases: eosinophilic granulomatosis with polyangiitis, inflammatory bowel disease
Adrenal insufficiency, some cancers (Hodgkin lymphoma)
Clonal disorders: myeloid neoplasms with eosinophilia, hypereosinophilic syndrome

Persistent hypereosinophilia can damage organs, especially the heart (endomyocardial fibrosis, thrombi), the lungs, skin and nerves. It needs specialist evaluation.

Low eosinophils

A low or zero count is common and usually harmless. It is typical during acute stress, infection, treatment with corticosteroids and in Cushing syndrome, because cortisol reduces circulating eosinophils within hours.

When to see a doctor

See a doctor if eosinophils are above 0.5 ×10⁹/L on repeated tests, or if they are raised together with rash, breathlessness, cough, diarrhoea or abdominal pain, weight loss or recent travel. Seek urgent care for a widespread rash with fever after starting a new medicine.

References

Valent P, Klion AD, Horny HP, et al. Contemporary consensus proposal on criteria and classification of eosinophilic disorders and related syndromes. J Allergy Clin Immunol. 2012;130(3):607–612.e9. doi:10.1016/j.jaci.2012.02.019
Blumenreich MS. The white blood cell and differential count. In: Walker HK, Hall WD, Hurst JW, eds. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd ed. Boston: Butterworths; 1990. Chapter 153. ncbi.nlm.nih.gov/books/NBK261
Chabot-Richards DS, George TI. Leukocytosis. Int J Lab Hematol. 2014;36(3):279–288. doi:10.1111/ijlh.12212

This article is for general information and does not replace a consultation with a doctor. Laboratory results must be interpreted by a physician together with symptoms and other tests.

Published on 26 April 2024

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