Value of laboratory studies in assessment of dehydration in children

Due to the lack of a reliable way of clinically measuring dehydration, laboratory tests are usually used to improve the accuracy of clinical assessment of dehydration in children. The purpose of this study was to compare the relationship between clinical and laboratory parameters in the assessment of dehydration and to evaluate the improvement of those parameters over time.

We conducted a retrospective study to assess the relationship between clinical assessment of dehydration and laboratory findings.

Three hundred children were eligible for the study. Twenty-six per cent of those with mild dehydration had serum urea concentrations greater than 14.3 mmol/L, compared with 38% and 5% of those with moderate or no dehydration, respectively. Urea concentration showed a good specificity, 95%. Creatinine concentrations and mean pH were similar whether or not dehydration was present. Bicarbonate and base excess concentrations decreased with the increasing severity of dehydration and were significantly greater in subjects with moderate dehydration than in those without. The sensitivity (71%) and specificity (74%) of both tests were rather poor. All groups had an abnormal anion gap, which was significantly greater in those with mild or moderate dehydration.

This study confirms that there is a discrepancy between clinical assessment and laboratory parameters of dehydration. Urea showed good specificity, and anion gap was the most sensitive laboratory parameter for assessment of dehydration. These findings need further validation.