Prevalence and Recovery of Euthyroid Sick Syndrome in Pediatric Diabetic Ketoacidosis: A Retrospective Cohort Study.

Background: Euthyroid sick syndrome (ESS) is a common finding in critically ill patients, including children with diabetic ketoacidosis (DKA). However, its prevalence, specific hormonal patterns, and recovery in the pediatric population remain inadequately characterized. This study aimed to determine the prevalence of ESS in pediatric DKA, characterize its hormonal subtypes, and identify factors associated with short-term thyroid function recovery. Methods: A retrospective cohort study was conducted involving 182 pediatric patients (0-18 years) with type 1 diabetes mellitus admitted for DKA between January 2023 and June 2025. Thyroid function tests (TSH, FT4, FT3) were measured at presentations and two weeks after DKA resolution. ESS was defined using age-specific reference ranges. Results: The prevalence of ESS at DKA presentation was 61.5% (112/182). Two distinct hormonal phenotypes were identified: isolated low FT3 (n = 40, 35.7%) and combined low FT4 and FT3 (n = 72, 64.3%). Patients with the isolated low FT3 pattern were significantly younger (median 9.5 [3.50, 11.00] vs. 12.0 [8.50, 14.00] years, p = 0.004) and had milder hormonal derangement than the combined group. Normalization of FT4 was significantly lower in children with severe DKA compared with those with mild/moderate disease (50.0% vs. 84.8%, p = 0.002). FT3 normalization was also reduced in the severe group (20.0% vs. 42.4%), although this difference did not reach statistical significance (p = 0.078). After 2 weeks, all ESS patients (100%) had achieved normal levels of at least one thyroid hormone, with 38.4% reaching normalization of FT3 and 36.6% achieving normalization of all measured thyroid parameters. Age (adjusted odds ratio [aOR] = 2.08, 95% confidence interval (CI): 1.57-3.06, p < 0.001) and baseline FT4 level (aOR = 2.14, 95% CI: 1.51-3.32, p < 0.001) were positive predictors for complete recovery. Conclusion: ESS is highly prevalent in pediatric DKA, with distinct phenotypic patterns associated with age and the severity of acute illness, particularly the degree of acidosis. While transient in nature, complete biochemical recovery within two weeks is not universal. These findings underscore that thyroid function tests during acute DKA should be interpreted with caution to avoid misdiagnosis of primary thyroid disease, and they support the critical practice of follow-up testing after metabolic stabilization instead of immediate hormone replacement.