Assessing children with gastroenteritis for evidence of dehydration is one of the most common things we do in acute paediatrics. For decades this has remained essentially a clinical task: blood tests often don't help, and we would usually start intravenous fluids anyway if doing a venepuncture. Authors from Alberta, Canada wondered how reliable clinical assessment is, and whether any non-invasive tests were better. They did a systematic review, looking for studies where …