• 2° to acute infection is most common cause of leucocytosis.

• Usually modest (uncommonly >30 x 109/L), associated with a left shift and occasionally toxic granulation or vacuolation of neutrophils.

• Chronic inflammation causes less marked neutrophilia often associated with monocytosis.

• Moderate neutrophilia may occur following steroid therapy, heatstroke and in patients with solid tumours.

• Mild neutrophilia may be induced by stress (e.g. immediate postoperative period) and exercise.

• May be seen in the immediate aftermath of a myocardial infarction or major seizure.

• Frequently found in states of chronic bone marrow stimulation (e.g. chronic haemolysis, ITP) and asplenia.

• Primary haematological causes of neutrophilia are less common. CML is often the cause of extremely high leucocyte counts (>200 x 109/L), predominantly neutrophils with marked left shift, basophilia and occa sional myeloblasts. A low LAP score and the presence of the Ph chromosome on karyotype analysis are usually helpful to differentiate CGL from a leukaemoid reaction.

• Less common are juvenile CML, transient leukaemoid reaction in Down syndrome, hereditary neutrophilia and chronic idiopathic neu-trophilia.

Bone marrow examination is rarely necessary in the investigation of a patient with isolated neutrophilia. Investigation of a leukaemoid reaction, leucoerythroblastic blood film and possible CGL or juvenile CML are firm indications for a bone marrow aspirate and trephine biopsy. Bone marrow culture, including culture for atypical mycobacteria and fungi, may be useful in patients with persistent pyrexia or leucocytosis.

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