Hyponatremia as a diagnostic marker for complicated appendicitis in children and adults: a retrospective cohort study

Introduction

This study aimed to evaluate the diagnostic performance of plasma sodium in identifying complicated appendicitis among pediatric and adult patients with appendicitis, and to compare its performance with conventional inflammatory markers.

Methods

A retrospective cohort study of all consecutive patients treated for appendicitis at Skåne University Hospital between 2022 and 2024. Disease severity was based on intraoperative and histopathological findings, or radiology in the case of non-operative management. The diagnostic performance of plasma sodium compared to conventional inflammatory markers (C-reactive protein, leukocytes and neutrophils) were evaluated using sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and area under the receiver operating characteristic curve (AUROC).

Results

1467 adults and 458 children were included. Complicated appendicitis was associated with higher inflammatory markers and lower plasma sodium levels in both children and adults. In children, plasma sodium <135 mmol/l yielded a specificity of 98.1 (95% c.i. 93.2–99.8) percent and a PPV of 94.6 (95% c.i. 81.2–98.6) percent. In the adult cohort, the specificity was 99.3 (95% c.i. 98.4–99.8) percent and PPV of 91.1 (95% c.i. 80.4–96.2) percent.

Plasma sodium demonstrated a moderate ability to discriminate complicated from uncomplicated appendicitis in both children (AUROC 0.719, 95% c.i. 0.656–0.783) and adults (AUROC 0.657, 95% c.i. 0.629–0.684). These AUROC:s were comparable to those for CRP, leukocytes and neutrophils.

Discussion

A plasma sodium <135 is a strong indicator of complicated appendicitis in both adult and pediatric patients. Plasma sodium should not be used as a sole indicator to rule out complicated disease.