Data source and study population

This study was a retrospective chart review of all paediatric (≤ 14 years old) patients with newly diagnosed T1DM. Electronic medical record data were collected from patients seen at the Department of Pediatric Endocrinology, Tongji Hospital, from January 2017 to December 2022. The inclusion criteria for T1DM followed the standards of medical care for diabetes of the American Diabetes Association [2, 13]. The diagnosis of DKA was based on recent International Society for Pediatric and Adolescent Diabetes guidelines: hyperglycaemia (blood glucose ≥ 11 mmol/L), metabolic acidosis (venous blood pH < 7.3 or serum bicarbonate < 15 mmol/L), and ketosis (presence of ketones in the blood or urine) [4, 14]. According to the WHO reference intervals, age- and gender- independent height and weight z-scores were calculated as previously described [15, 16]. Body mass index (BMI) was calculated as weight (kg)/height (m²), and was converted to a BMI Z-score according to the LMS method: Z = [(BMI/M)L − 1]/(L × S) [the median (M), coefficient of variation (S) and skewness (L)] [17]. Obesity was defined as ≥ 95th percentile of gender-specific BMI according to the growth charts of children in China [18]. The incidence of T1DM was calculated by summing the numbers of children and adolescents newly diagnosed in Tongji hospital each year, and then dividing by the total general population (≤ 14 years old) in Hubei Province, China (the data are mainly collected from Hubei Statistical Yearbook, http://tjj.hubei.gov.cn/).