Leukaemoid Reaction

Key points

• The leukaemoid reaction describes the presence of immature cells (myeloblasts, promyelocytes, nucleated red cells) in the peripheral blood
• Causes: severe infection, severe haemolysis, massive haemorrhage, metastatic cancer with bone marrow infiltration
• Differentiating from chronic myeloid leukaemia: leukaemoid reaction shows a high leucocyte alkaline phosphatase (LAP) score, whereas CML shows a low LAP score
• Toxic granulation, Döhle bodies and cytoplasmic vacuolation favour a reactive leukaemoid reaction over CML