Phosphate metabolism in red blood cells of critically ill neonates

Very few data exist on phosphate metabolism in critically ill neonates. Therefore we studied the incidence of hypophosphataemia, the intracellular metabolism of phosphate by measuring adenosine 5'-triphosphate (ATP) and 2,3-diphosphoglycerate (2,3-DPG) in red blood cells, and excretion of phosphate in urine. The aims of the study were early detection of changes in phosphate metabolism as possible diagnostic markers of sepsis and defining the cause of hypophosphataemia. Neonates, treated in multidisciplinary paediatric intensive care unit (PICU), included in the study, were less than three days of age. Eighteen of them had respiratory distress syndrome (RDS) and 16 had microbiologically confirmed or clinical sepsis. The overall incidence of hypophosphataemia in critically ill neonates was over 80%, and was more common (88%) and more profound in those with sepsis than in those with RDS (79%). Therefore the septic neonates needed significantly larger amounts of phosphate to maintain normophosphataemia. In septic neonates ATP concentration in red blood cells was significantly lower than in neonates with RDS and controls, while the 2,3-DPG concentration was increased as a result of compensation. In septic neonates urinary losses of inorganic phosphate (Pi) were significantly higher than in neonates with RDS. Hypophosphataemia in critically ill neonates is at least partly due to higher urinary losses of phosphate.