Outcome of extremely low birth weight infants with leukemoid reaction.

BACKGROUND: Leukemoid reaction (LR) is defined as an absolute neutrophil count (ANC) of >30 x 10(3)/mm(3). No previous study has systemically examined the clinical and prognostic significance of this phenomenon in extremely low birth weight (ELBW) infants.

OBJECTIVE: The purpose of this study was to examine the effect of LR in morbidity, mortality, and long-term developmental outcome in ELBW infants.

METHOD: Infants with gestational age of <or=30 weeks and birth weight <or=1000 g were included in the study (n = 152). The medical records were reviewed for the clinical characteristics and long-term developmental outcome of these infants. Serial complete blood cell count and ANC were calculated on day 1 and weekly thereafter until discharge. LR was defined as an ANC of >30 x 10(3)/mm(3).

RESULTS: LR was detected in 17% of the study infants (26 of 152). ANC increased postnatally in LR (n = 26) and no-LR (n = 126) infants during hospitalization, peaked in the second week of life (43 +/- 3 vs 14 +/- 1 x 10(3)/mm(3)), and remained significantly higher in LR infants during the first 5 weeks of life. LR occurred more frequently during the first 2 weeks of life and lasted for 3 +/- 1 days. There was no significant difference between the LR and no-LR infants in gestational age, birth weight, delivery mode, gender, Apgar scores, or incidence of respiratory distress syndrome, patent ductus arteriosus, necrotizing enterocolitis, intraventricular hemorrhage, and retinopathy of prematurity. LR infants required a significantly longer duration of ventilatory support (36 +/- 4 vs 21 +/- 2 days), longer duration of oxygen requirement (58 +/- 6 vs 40 +/- 3 days), and had a higher incidence of bronchopulmonary dysplasia (BPD) (54% vs 25%) compared with no-LR infants. Furthermore, the length of hospitalization was significantly longer in LR infants (69 +/- 6 vs 54 +/- 3 days). There was no significant difference between the groups in developmental outcome at 2 years of age including receptive/expressive language, fine/gross motor skills, and hearing. Incidence of abnormal neurodevelopment outcome was also similar between LR and no-LR infants.

CONCLUSIONS: LR in ELBW infants is associated with a prolonged need for ventilatory and oxygen support, a higher incidence of BPD, and a tendency for lower mortality. The findings from our study suggest that LR is associated with conditions known to have an excess of proinflammatory cytokines. Additional prospective study is needed to understand the relationship between LR, proinflammatory cytokines, and development of BPD.