Professional Reference articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.

The main functions of eosinophils include involvement in defence against parasites, allergic responses, tissue inflammation and immunity. Eosinophilia is a peripheral eosinophil count greater than the upper limit of normal range, usually around 0.45 x 109/L. In many cases the cause is clear - eg, atopic disease. However, the differential diagnosis includes many serious diseases, including malignancy.

  • In the UK, eosinophilia is most often due to allergic conditions.
  • Worldwide, helminth infections are the most common cause of eosinophilia.[1]
  • Travel history to assess whether a patient has travelled to an area that is endemic for certain infections, including helminthic infections.
  • Medication and diet history to evaluate for allergic reactions associated with eosinophilia.
  • History of symptoms associated with possible underlying causes (see 'Causes', below).
  • A complete physical examination is required because diseases associated with eosinophilia can involve any part of the body.

Investigation is guided by the history, examination, and clinical picture and may include:

  • FBC, including differential white cell count.
  • Renal function tests, LFTs.
  • Urine tests: all patients with blood eosinophilia and haematuria and who have been in Africa should have their urine examined for the eggs of Schistosoma haematobium. Cystoscopy may be required to confirm the diagnosis.
  • Lumbar puncture: CSF eosinophilia due to worm infections (eg, Angiostrongylus cantonensis), drug reactions, and coccidioidomycosis meningitis.
  • CT scans of the lungs, abdomen, pelvis, and brain evaluate for focal defects due to diverse causes of eosinophilia - eg:
    • Worm infections of the liver (eg, Fasciola hepatica) can cause focal hepatic lesions.
    • Coccidioidomycosis can cause focal lesions in the lung, which are visible on CXR or CT scan.
    • Hodgkin's lymphoma or non-Hodgkin's lymphoma can cause lymphadenopathy in the abdomen, which can be seen on a CT scan.
  • Echocardiogram to assess for thrombi (eg, mural, endocardial) due to hypereosinophilic syndrome.
  • Bone marrow biopsy may be required.

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  1. Mejia R, Nutman TB; Evaluation and differential diagnosis of marked, persistent eosinophilia. Semin Hematol. 2012 Apr 49(2):149-59. doi: 10.1053/j.seminhematol.2012.01.006.
  2. Simon D, Simon HU; Eosinophilic disorders. J Allergy Clin Immunol. 2007 Jun 119(6):1291-300
  3. Pagnoux C, Guilpain P, Guillevin L; Churg-Strauss syndrome. Curr Opin Rheumatol. 2007 Jan 19(1):25-32.
  4. Eosinophilic fasciitis; DermNet NZ
Dr Mary Harding
Peer Reviewer:
Dr John Cox
Document ID:
2100 (v25)
Last Checked:
12 March 2014
Next Review:
11 March 2019

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. Patient Platform Limited has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.