Elevated WBC

Leucocytosis is defined as elevation of the white cell count >2 SD above the mean. The detection of leucocytosis should prompt immediate 14 scrutiny of the automated WBC differential (generally accurate except in leukaemia) and the other FBC parameters. Blood film should be examined and a manual differential count performed. Important to evaluate leucocytosis in terms of the age-related absolute normal ranges for neutrophils, lymphocytes, monocytes, eosinophils and basophils (ffl p688, 690) and the presence of abnormal cells: immature granulocytes, blasts, nucleated red cells and 'atypical cells'.

Leukaemoid reaction—leucocytosis >50 x 109/L defines a neutrophilia with marked 'left shift' (band forms, metamyelocytes, myelocytes and occasionally promyelocytes and myeloblasts in the blood film). Differential diagnosis is chronic granulocytic leukaemia (CGL) and in children, juvenile CML. Primitive granulocyte precursors are also frequently seen in the blood film of the infected or stressed neonate, and any seriously ill patient e.g. on ITU.

Leucoerythroblastic blood film—contains myelocytes, other primitive granulocytes, nucleated red cells and often tear drop red cells, is due to bone marrow invasion by tumour, fibrosis or granuloma formation and is an indication for a bone marrow biopsy. Other causes include anorexia and haemolysis.

Leucocytosis due to blasts—suggests diagnosis of acute leukaemia and is an indication for cell typing studies and bone marrow examination.

FBC, blood film, white cell differential count and the clinical context in which the leucocytosis is detected will usually indicate whether this is due to a 1° haematological abnormality or reflects a 2° response.

^ It is clearly important to seek a history of symptoms of infection and examine the patient for signs of infection or an underlying haematological disorder.

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