Leukemoid reaction in extremely low-birth-weight infants

The objective of this paper was to determine the incidence of leukemoid reaction and to evaluate its relationship with maternal and neonatal factors in extremely low-birth-weight (ELBW) infants. The design a case-controlled retrospective study of all live-born ELBW infants (<1000 g) over a period of 2 years, from July 1994 to June 1996. A total of 60 preterm infants were born during the study period, and are included in this report. The infants who demonstrated leukemoid reaction formed the study group, while the remainder formed the control group. Leukemoid reaction was defined as a white blood cell (WBC) count ≥50,000/mm³. The relationship between maternal and neonatal variables and WBC counts was studied. Nine of the 60 infants studied demonstrated counts >50,000/mm³, with an incidence of 15%. There was no significant association demonstrated between maternal or neonatal variables and leukemoid reaction. Patients with leukemoid reaction had a better overall survival. Leukemoid reaction in ELBW infants is a rare and recently documented phenomenon. In our study the incidence was 15%. Although many factors have been postulated as a cause of this phenomenon, we could not demonstrate any relationship between these factors and high WBC counts, including sepsis and the use of antenatal steroids, the two most likely variables. It was interesting to note that the infants who were able to mount a leukemoid response had a better chance of survival than those who did not.