Postnatal persistence of capillary-venous differences in hematocrit and hemoglobin values in low-birth-weight and term infants.

Full-term and preterm infants were studied to determine whether differences between capillary and venous hematocrit and hemoglobin values were detectable after the first week of life. Significant differences were shown to persist in both term and preterm infants into at least the third postnatal months. However, the differences were considerably greater in low-birth-weight infants, with mean capillary values at ages 4 to 6 postnatal weeks approximately 11% to 12% higher than the corresponding venous values. The data indicated that capillary-venous differences were related not only to postnatal age, but also the postconceptual age.