The Utility of Copeptin Measurement in Hospitalized Pediatric Patients with Syndrome of Inappropriate Antidiuretic Secretion.

Introduction: Hyponatremia is common in hospitalized pediatric patients, and in many cases, the diagnosis of the syndrome of inappropriate antidiuretic secretion (SIADH) remains challenging, with no gold standard for diagnosis. We assessed factors associated with hyponatremia in pediatric patients clinically diagnosed with SIADH and examined the validity of copeptin level as a useful tool to distinguish SIADH from non-SIADH causes of hyponatremia.

Methods: This observational study retrospectively analyzed 19 patients admitted to Children's Hospital of Orange County in 2021-2024 for hyponatremia. ROC analyses assessed the ability of copeptin level to distinguish diagnostic groups, determining the optimal threshold for classification.

Results: Pediatric patients with a diagnosis of SIADH had a significantly higher average urine sodium level (135.4 vs. 68.3, p = 0.036) and higher average copeptin level (median = 14.3 vs. 5.7, p = 0.036). ROC analyses determined copeptin had good ability to differentiate a clinical diagnosis of SIADH from non-SIADH causes of hyponatremia with sensitivity 83%, specificity 71%, PVP 83%, NPV 71%. A significantly higher percentage of patients with copeptin level greater than 8.0 pmol/L were diagnosed with SIADH (83.3% vs. 28.6%, p = 0.017).

Conclusion: Copeptin levels correlated with a clinical diagnosis of SIADH in hospitalized pediatric patients, particularly if elevated above 8.0 pmol/L at the time of hyponatremia, and the patient met the Schwartz and Bartter clinical criteria for SIADH. However, in some cases of SIADH, copeptin levels may be in normal range and could be considered inappropriately high for the degree of hyponatremia.