How accurate is glucose analysis in the presence of multiple interfering substances in the neonate? (glucose analysis and interfering substances)

Whole blood glucose testing by reagent sticks is inaccurate at low plasma glucose concentrations and with varying hematocrit. Both conditions are frequently seen in newborn infants. Therefore plasma glucose analysis is the preferred method for newborn glucose monitoring. We encountered unanticipated difficulties in plasma glucose measurement by the automated hexokinase method caused by the combinations of plasma free hemoglobin, bilirubin, and plasma triglycerides, which are frequently elevated in newborn plasma. We determined the adverse effects of various combinations of these interfering substances on glucose analysis by the hexokinase method and demonstrated that accurate analysis is possible by a 1:1 plasma dilution only at high plasma glucose levels but not at the more critical low plasma glucose concentration. The dilution reduced the number of repeat specimens required in newborns. But 1:1 plasma dilution overestimated the glucose levels at low plasma glucose values, and therefore this automated hexokinase method is not suitable for glucose analysis in the newborn. Glucose-oxidase remains the method of choice for plasma glucose analysis in neonates. This information is important because using this hexokinase methodology, one might miss hypoglycemia in the newborn.