Low Plasma Sodium Concentration Predicts Perforated Acute Appendicitis in Children: A Prospective Diagnostic Accuracy Study.

INTRODUCTION: Early differentiation between perforated and nonperforated acute appendicitis (AA) in children is of major benefit for the selection of proper treatment. Based on pilot study data, we hypothesized that plasma sodium concentration at hospital admission is a diagnostic marker for perforation in children with AA. MATERIALS AND METHODS: This was a prospective diagnostic accuracy study, including previously healthy children, 1 to 14 years of age, with AA. Blood sampling included plasma sodium concentration, plasma glucose, base excess, white blood cell count, plasma arginine vasopressin (AVP), and C-reactive protein. RESULTS: Eighty children with histopathologically confirmed AA were included in the study. Median plasma sodium concentration on admission in patients with perforated AA (134 mmol/L, [interquartile range 132-136]) was significantly lower than in children with nonperforated AA (139 mmol/L, [137-140]). The receiver operating characteristic curve of plasma sodium concentration identifying patients with perforated AA showed an area under the curve of 0.93 (95% confidence interval, 0.87-0.99), with a sensitivity and specificity of 0.82 (0.70-0.90) and 0.87 (0.60-0.98), respectively. Plasma sodium concentrations ≤136 mmol/L resulted in an odds ratio of 31.9 (6.3-161.9) for perforation. The association between low plasma sodium concentration and perforated AA was confirmed in a multivariate logistic regression analysis. Median plasma AVP on admission was higher in patients with perforated (8.6 pg/mL [5.0-14.6]) as compared with nonperforated AA (3.4 pg/mL [2.5-6.6]). CONCLUSION: In children with AA, there is a strong association between low plasma sodium concentration and perforation, a novel and not previously described finding.