Clinical Utility of 30-Min Postload Plasma Glucose in Paediatric Obesity

Introduction: Intermediary glucose measurements at other time points in a standard 2-hour oral glucose tolerance test (OGTT) is increasingly being investigated, and a number of studies have demonstated strong predictive value of 1-hour plasma glucose (PG) in identifying subjects with high risk of future diabetes and vascular complications. The association between 30-minute PG and incidence of diabetes is less extensively studied and all the suggested 30-minute PG cutoff values in current literature are derived from adult population. Our study aimed to evaluate the optimal cutoff value of 30-minute PG in predicting abnormal OGTT (prediabetes/diabetes) in a cohort of paediatric subjects with overweight or obesity. Since 30-minute PG could be easily performed even in a busy clinic setting, such cutoff allows clinicians identify high risk subjects who should proceed to a 2-hour OGTT. Methods: Record of 332 paediatric subjects with overweight/obesity who had OGTT done in a tertiary unit from January 2012 to December 2018 was reviewed. Standard OGTT was performed and blood samples for PG and insulin were obtained at 0 minute, 30 minutes and 120 minutes. Subjects with prediabetic and diabetic response were considered together as a group (abnormal OGTT group) for statistical analysis. 30-min PG and insulinogenic index (IGI) were compared, and 30-min PG cutoff which predicts abnormal OGTT response was derived. Results: Our cohort consists of 97.3% Chinese with mean age of 15.4 ± 2.3 years and mean BMI z-score of 2.7 ± 0.6. Sixty subjects (18.1%) had abnormal OGTT – out of which 47 (14.2%) and 13 (3.9%) had prediabetes and diabetes range of glycaemic response respectively. 30-minute PG was statistically higher in the abnormal OGTT group compared to the normal OGTT group (9.6 vs 7.9 mmol/L, p=0.001). IGI was statistically lower in the abnormal OGTT group compared to the normal group (262.1 vs 377.2, p=0003). 30-min PG ≥ 9.2 mmol/L predicts abnormal OGTT with best combination of sensitivity and specficity (AUC 0.77, sensitivty 62.1%, specificity 83.7%). Conclusion: Children with abnormal OGTT reseponse showed impaired first phase insulin secretion suggestive of beta-cell loss. Instead of performing a 2-hour OGTT in every child referred for obesity, 30-min PG, with a cutoff value of 9.2mmol/L, could be used as a stratification tool in identifying high risk subjects who should return for a 2-hour OGTT in another visit.