INCIDENCE, SIGNIFICANCE, AND KINETIC MECHANISM RESPONSIBLE FOR LEUKEMOID REACTIONS IN PATIENTS IN THE NEONATAL INTENSIVE-CARE UNIT - A PROSPECTIVE EVALUATION

Objective: To prospectively investigate the incidence, significance, a nd kinetic mechanism responsible for leukemoid reactions in patients i n the neonatal intensive care unit (NICU). Design: We prospectively st udied all infants admitted to the NICU at the University of Florida wh o, during a period of 12 consecutive months, had a leukemoid reaction. All those identified had a standardized evaluation consisting of (1) karyotype analysis, (2) bacterial cultures, (3) evaluations for toxopl asmosis, other (congenital syphilis and viruses), rubella, cytomegalov irus, and herpes simplex virus) (TORCH), (4) determination of blood vi scosity, (5) use of marrow aspirates for morphology, clonogenic progen itor cell assays, and cell-cycle analysis of progenitors, (6) determin ation of serum concentrations of granulocyte and granulocyte-macrophag e colony-stimulating factors, and (7) serial complete blood cell count s until the leukemoid reaction remitted. Results: During 12 months, 70 7 patients were admitted to the NICU and 4262 complete blood cell coun ts were performed on samples from these patients. A leukemoid reaction was identified in nine patients, all of whom were preterm (born at 24 to 38 weeks' gestation), Peak blood;leukocyte concentrations were 51. 7+/-15.6x10(3)/mu l (mean+/-SD). The leukemoid reactions were detected during the first 4 days of life in seven patients, on day 9 in one, a nd on day 25 in one. An abnormal karyotype (47,XY,+21) was present in one infant. Mothers of four infants had received betamethasone antenat ally. None had elevated whole blood viscosity or positive findings on bacterial or TORCH evaluations. None of the bone marrow findings were consistent with steroid-induced leukocytosis; all studies indicated ac celerated neutrophil production. Serum concentrations of granulocyte-m acrophage colony-stimulating factor were either negligible or nondetec table. Serum granulocyte colony-stimulating factor was elevated in thr ee patients, low in two, and nondetectable in four. The leukemoid reac tions persisted for 5 to 32 days, the longest being in the patient wit h trisomy 21.