Abstract
Hypernatraemia in children is uncommon beyond the immediate neonatal period and may have many causes. The interpretation of biochemical measurements in these patients can be difficult. In 2009, the Royal College of Paediatrics and Child Health (RCPCH) issued guidelines on the differential diagnosis of hypernatraemia and highlighted the need to collect paired serum and urine samples in these patients to aid diagnosis.
Forma et al. present an excellent retrospective study investigating the causes and the biochemical differences between children who were found to be hypernatraemic on admission to hospital. Patients with a sodium concentration >150 mmol/L and aged between two weeks and 17 y were identified from laboratory records. Patient notes were reviewed and the following data collated: timing of hypernatraemia in relation to admission; cause of hypernatraemia (if known) and any evidence of contamination of sample; serum urea and creatinine, urine sodium, creatinine and osmolality.
Following exclusions, a total of 45 patients presented to hospital with hypernatraemia. The most common cause was dehydration secondary to either gastroenteritis or systemic infection. A further 177 patients developed hypernatraemia during their hospital admission. The most common cause was dehydration secondary to systemic infection, usually in patients with cerebral palsy. The next most common cause was postoperative cardiac surgery. One case of salt poisoning (11 separate episodes) and one case of osmoreceptor dysfunction (5 separate episodes) were found.
The majority (88%) of patients with dehydration had a urea concentration above the upper limit of normal. The two patients with osmoreceptor dysfunction and salt poisoning both had normal urea concentrations for each of their multiple episodes. Urine sodium was markedly higher in the case of salt poisoning than for other patients. Urine creatinine tended to be generally lower in salt poisoning, with urine osmolality approximately the same in all three causes of hypernatraemia. Both the urine sodium:creatinine ratio and fractional excretion of sodium were much higher in the case of salt poisoning when compared with other aetiologies.
This study provides useful data into the incidence of hypernatraemia in the paediatric population and the biochemical differences between aetiologies. The study also confirms the need for paired serum and urine samples to be collected as soon as possible in order to expedite a diagnosis of salt poisoning as suggested by the RCPCH guidelines.