Can Quantab titrator sticks reliably predict urinary sodium in people with suspected dehydration

A point of care test for urinary sodium, a commonly used measure of dehydration, may reduce delays in clinical decision making by offering more timely guidance leading to improved fluid management. We compared laboratory assessed urinary sodium with a potential point of care measure of urinary chloride in people with suspected dehydration, to explore its use as an indicator of dehydration.Urinary chloride concentrations were estimated using a Quantab titrator stick in samples from a variety of patient groups that had been sent for urinary sodium assays. We validated the results of this titrator stick with laboratory-assessed sodium concentrations by deriving correlation coefficients between these methods and using limits of agreement testing. We determined the optimal titrator stick cut-point for identifying biochemical dehydration (urinary sodium < 20 mmol/L) by maximising the product of the sensitivity and specificity.We obtained laboratory urinary sodium concentration and Quantab stick chloride measures on 127 samples. Twenty three percent were biochemically dehydrated. A threshold of <4.3 on the Quantab scale had a positive predictive value for biochemical dehydration of 56% (95%CI 40%–71%) and a negative predictive value of 94% (95%CI 87%–98%).These data suggest that the Quantab stick could be used as a point of care test to aid fluid management decisions. Further work to explore the use of the titrator stick in specific patient populations is justified.