Challenges in using fractional excretion of sodium in the assessment of salt poisoning

Abstract

Aim: Hypernatraemia typically reflects dehydration, yet in rare instances may be caused by salt poisoning. Identifying these rare cases is a difficult challenge. Making the diagnosis of salt poisoning can have severe consequences, such as the removal of the child from its home or even prison sentences for the implicated carer. It is therefore imperative to get the diagnosis right. Guidelines for the assessment of hypernatraemia emphasise the importance of the fractional excretion of sodium to distinguish between dehydration and salt poisoning, but no generally accepted cut-off value exists. Opinions about the diagnosis of salt poisoning in some cases consequently may differ. Here, we aim to highlight the challenges and stimulate discussion on how to improve the tools for the assessment of hypernatraemia. Methods: Report of a case of unexplained hypernatraemia in which the treating paediatrician raised the suspicion of salt poisoning. Results: Two consulted experts made opposing judgements about the aetiology of the observed hypernatraemia. Conclusion: Clear diagnostic criteria for the diagnosis of salt poisoning are lacking and more data are needed for their establishment. Without this, victims may experience further harm and carers are at risk of devastating, yet potentially erroneous accusations.