Usefulness of serum sodium levels as a novel marker for predicting acute appendicitis severity: a retrospective cohort study

Background: Early and accurate preoperative diagnosis of complicated appendicitis mandates the identification of new markers. The aim of this study is to determine whether preoperative serum sodium levels are useful for predicting the severity of acute appendicitis. Methods: We retrospectively analyzed 475 patients who underwent emergency appendectomies between January 2018 and February 2023 in a general hospital in Brazil. The patients were divided into 2 groups: complicated (n = 254) and uncomplicated (n = 221). Hyponatremia was defined as serum sodium levels < 136 mEq/L. The primary outcome was to evaluate if hyponatremia is associated with complicated appendicitis. Results: The patients had a median age of 22 years, and the median serum sodium level was 137 mEq/L in patients with complicated appendicitis and 139 mEq/L in uncomplicated appendicitis (P < 0.001). The analysis of the receiver operating characteristic curve used as the best cutoff value of serum sodium of 136 mEq/L with a sensitivity of 45.7%, specificity of 86.4%, positive predictive value of 79.5%, and negative predictive value of 58.1% for the diagnosis of complicated AA. Of the 254 patients with complicated appendicitis, 84 (33.1%) had serum sodium levels below 136 mEq/L, while only 12 (5.4%) patients with uncomplicated appendicitis had values ​​below this cutoff. Patients with hyponatremia were 5 times more likely to develop complicated appendicitis. (odds ratio: 5.35; 95% confidence interval: 3.39–8.45) Conclusions: Preoperative serum sodium levels are a useful tool for predicting the severity of acute appendicitis. Due to its low cost and wide availability, it has become an extremely relevant marker.