Practice Rational Testing

Investigation of an incidental finding of eosinophilia

BMJ 2011; 342 doi: (Published 18 May 2011) Cite this as: BMJ 2011;342:d2670
  1. Hannah Sims, haematology specialist registrar,
  2. Wendy N Erber, consultant haematologist
  1. 1Haematology Department, Addenbrooke’s Hospital, Cambridge CB2 0QQ, UK
  1. Correspondence to: Professor Wendy N Erber, Pathology and Laboratory Medicine, M504, University of Western Australia, 35 Stirling Highway, Nedlands WA 6009, Australia werber{at}

The causes of eosinophilia fall into three categories (reactive disorders, clonal disorders of the bone marrow, and hypereosinophilic syndrome). This article outlines the appropriate use of investigations to establish the cause of eosinophilia

Learning points

  • When eosinophilia is found, ensure that a blood film has been reviewed. This can give insight into the underlying aetiology

  • If the eosinophil morphology is normal or the blood film appearances favour a reactive (secondary) cause the patient should be reviewed to establish the likely aetiology

  • Persistence of eosinophilia >1.5×109/L for three months or a rising eosinophil count without an obvious cause warrants referral to a haematologist

A 57 year old man presented to his general practitioner with symptoms of a persistent dry cough and general fatigue. He had no notable medical history; he was a non-smoker and was not taking any regular medication. Clinical examination was unremarkable. A full blood count showed haemoglobin 141 g/L (normal range 130-180 g/L), mean cell volume 92 fL (80-100 fL), platelets 178×109/L (150-400×109/L), and leucocytes 9×109/L (4-13×109/L). The leucocyte differential showed neutrophils 4.3×109/L (2-8×109/L), lymphocytes 3×109/L (1-4×109/L), monocytes 0.5×109/L (0.2-0.8×109/L), and eosinophils 8.2×109/L (0.1-0.6×109/L). The blood film confirmed the presence of the eosinophilia and the eosinophil morphology appeared normal. Red cells, other leucocytes, and platelets were also morphologically normal. On the basis of the blood appearances the reporting haematologist favoured a reactive cause for the eosinophilia (such as infection, allergy, and hypersensitivity disorders; vasculitis; and autoimmune disorders). …

View Full Text

Sign in

Log in through your institution

Free trial

Register for a free trial to to receive unlimited access to all content on for 14 days.
Sign up for a free trial