Leukaemoid reaction

The leukaemoid reaction describes the presence of immature cells such as myeloblasts, promyelocytes and nucleated red cells in the peripheral blood. This may be due to infiltration of the bone marrow causing the immature cells to be 'pushed out' or sudden demand for new cells

Causes

• severe infection
• severe haemolysis
• massive haemorrhage
• metastatic cancer with bone marrow infiltration

A relatively common clinical problem is differentiating chronic myeloid leukaemia from a leukaemoid reaction. The following differences may help:

Leukaemoid reaction

• high leucocyte alkaline phosphatase score
• toxic granulation (Dohle bodies) in the white cells
  • blue-grey, oval cytoplasmic inclusions found in neutrophils during toxic states or infections.
• 'left shift' of neutrophils i.e. three or fewer segments of the nucleus

Chronic myeloid leukaemia

• low leucocyte alkaline phosphatase score

Leukemoid reaction

Profound leukocytosis > 50

characterized by a significant increase in early neutrophil precursors in the peripheral blood

it is the response of normal bone marrow to cytokine release by lymphocytes, macrophages and other cells in response to infection or trauma

marked "left shift", increased numbers of band forms and sometimes even myelocytes and metamyelocytes in peripheral film.