Reference ranges for hematocrit and blood hemoglobin concentration during the neonatal period: data from a multihospital health care system.

OBJECTIVE "Reference ranges" are developed when it is impossible or inappropriate to establish "normal ranges" by drawing blood on healthy normal volunteers. Reference ranges for the hematocrit and the blood hemoglobin concentration of newborn infants have previously been reported from relatively small sample sizes by using measurement methods that now are considered outmoded. METHODS We sought to develop reference ranges for hematocrit and hemoglobin during the neonatal period (28 days) by using very large sample sizes and modern hematology analyzers, accounting for gestational and postnatal age and gender. Data were assembled from a multihospital health care system after exclusion of patients with a high likelihood of an abnormal value and those who were receiving blood transfusions. RESULTS During the interval from 22 to 40 weeks' gestation, the hematocrit and blood hemoglobin concentration increased approximately linearly. For every week advance in gestational age, the hematocrit increased by 0.64% and the hemoglobin concentration increased by 0.21 g/dL. No difference was seen on the basis of gender. During the 4-hour interval after birth, hematocrit/hemoglobin values of late preterm and term neonates (35-42 weeks' gestation) increased by 3.6% +/- 0.5% (mean +/- SD), those of neonates of 29 to 34 weeks' gestation remained unchanged, and those of <29 weeks' gestation decreased by 6.0% +/- 0.3%. During the first 28 days after birth, an approximately linear decrease in hematocrit/hemoglobin occurred. CONCLUSIONS The figures presented herein describe reference ranges for hematocrit and blood hemoglobin concentration during the neonatal period, accounting for gestational and postnatal age.