Beyond the umbilical cord: interpreting laboratory tests in the neonate

Interpretation of biochemical testing in the neonatal period is challenging because of the complexity of perinatal physiology, the difficulty of establishing appropriate laboratory reference ranges, and the technical aspects of analyzing microvolume specimens that are often hemolyzed, lipemic, or have a high hematocrit or bilirubin concentration. Metabolic problems such as hyperbilirubinemia and hypoglycemia in the full-term neonate occur as the infant adapts from an intrauterine metabolism to extrauterine life. Pathophysiological processes in the premature infant vary with the severity of prematurity and the immaturity of metabolic systems. Interpreting neonatal biochemistry requires age- and gestation-specific reference ranges but technical, ethical, and philosophical concerns continue to impair the development of the needed reference data.