Endocrine Abstracts

Background: Childhood obesity and type 2 diabetes mellitus (T2DM) have increased proportionately in the last decade. Oral glucose tolerance test (OGTT) is recommended for paediatric patients with a BMI >98th centile (NICE, 2014) to identify T2DM or abnormal glucose homeostasis (AGH).

Aim: To estimate the proportion of patients with AGH/T2DM seen in a tier 3 obesity service and evaluate the utility of the glycated haemoglobin (HbA1C) in detecting AGH.

Methods: Retrospective data were collected from children and young people (CYP) with obesity undergoing an OGTT between 2015-2020. Fasting blood glucose (FBG), 2 h post-prandial glucose (PPG), fasting insulin and HbA1C were recorded. Any clinical features of insulin resistance were documented. OGTT results were interpreted using WHO (2006) criteria.

Results: Of 113 CYP (mean age 13.2 years), 52 were male and mean body mass index (BMI) was 32.1 kg/m2 (+2.77SDS). 6 patients (5.3%, 5 Caucasian, 1 Black African ethnicity) were diagnosed with T2DM. 5 (4.5%) had impaired glucose tolerance (IGT) (2-hour PPG 7.8-11 mmol/l) and 1 (1%) had both impaired fasting glycaemia (IFG) (FBG 6.1-6.9 mmol/l) and IGT. 101 patients (90%) had a normal OGTT. Median HbA1C at diagnosis was 53.5 mmol/mol (49-94) for those with T2DM and 40 mmol/mol (33-45 mmol/mol) for those with for those with IFG/IGT. HbA1c ≥ 48 mmol/l was predictive of T2DM with sensitivity 100% (95% CI 54.1 - 100), specificity 100% (95% CI 96.6 - 100) and positive predictive value (PPV) of 85.7% (95% CI 46.0 -97.7). HbA1c > 43 mmol/mol was predictive of detecting AGH with sensitivity 66.7% (95% CI 34 - 90), and specificity 97.0% (95% CI 93.03 - 99.76). In patients with normal OGTT average HbA1C was 37 mmol/mol (range = 29-44 mmol/mol). HbA1c ≤39 was predictive of normal OGTT with sensitivity 85.3% (95% CI 76.5 – 91.7) and specificity 83.3% (95% CI 58.6 – 96.4).The number-needed-to-screen for one patient to be diagnosed with T2DM or AGH was 28 and 10 respectively.

Conclusion: HbA1C could be considered as a screening tool in CYP with obesity to indicate the requirement for OGTT to detect AGH, potentially avoiding the clinical and cost burden of an invasive test.