Extreme hyperleucocytosis of the premature.

Physiological leucocytosis is common in neonates. Leukemoid reaction is defined as a variable degree of leucocytosis with immature precursors, similar to that occurring in leukaemia but because of other causes. Leukemoid reactions are well-recognised in the neonatal intensive care unit population and are associated with antenatal corticosteroids, Down's syndrome, chorioamnionitis, funisitis and perinatal infections. However, extreme hyperleucocytosis, exceeding a white blood cell count of 100×10(9)/l is rare. In the 7-year period from 2005 to 2012 three premature infants in our hospital presented with extreme hyperleucocytosis. Since there were no signs of neonatal leukaemia, transient myeloid disorder or leucocyte adhesion defect, a leukemoid reaction owing to antenatal corticosteroids, chorioamnionitis and funisitis was diagnosed. No obvious complications of hyperleucocytosis were observed. Therapy was not necessary and the leucocytes normalised spontaneously. In our small case series, extreme hyperleucocytosis in prematures occurred in the absence of leukaemia and had a mild course.