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Medical Professionals

Professional Reference articles are designed for health professionals to use. They are written by UK doctors and based on research evidence, UK and European Guidelines. You may find one of our health articles more useful.

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.

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  • In the UK, eosinophilia is most often due to allergic conditions.

  • Worldwide, helminth infections are the most common cause of eosinophilia1.


  • 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.

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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.

Further reading and references

  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; quiz 1301-2. Epub 2007 Apr 2.
  3. Pagnoux C, Guilpain P, Guillevin L; Churg-Strauss syndrome. Curr Opin Rheumatol. 2007 Jan;19(1):25-32.
  4. Eosinophilic fasciitis; DermNet NZ

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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