Comparison of glycated haemoglobin and fasting blood glucose in the diagnosis of diabetes mellitus and pre-diabetes in a cohort of obese patients

Abstract

Diabetes mellitus (DM) has historically been diagnosed by measurement of blood glucose concentrations. More recently, the use of glycated haemoglobin (HbA1c) has been advocated in the diagnosis of diabetes, complementing its existing role in the monitoring of glycaemic control. A recent study has shown that obesity is an important problem in the UK Armed Forces. Obese patients are at increased risk of diabetes and intermediate hyperglycaemia (pre-diabetes). It is unclear whether the application of diagnostic criteria based on HbA1c would produce different categorisation of obese patients compared with standard glucose-based criteria. In the current study, we compared HbA1c with fasting plasma glucose in the diagnosis of type 2 diabetes and intermediate hyperglycaemia in a cohort of obese patients. Patients were recruited from the NHS Tayside Specialist Weight Management Service. They were classified into three categories (normoglycaemia, pre-diabetes, and diabetes) according to their fasting plasma glucose (FPG) and HbA1c. The diagnostic criteria of three organisations were applied: the World Health Organisation (WHO); the American Diabetes Association (ADA); and the International Expert Committee (IEC). Glucose, insulin, cholesterol, triglycerides, uric acid, liver function tests and sex hormone-binding globulin (SHBG) were measured. By WHO (fasting glucose) criteria, 102 subjects were classified as normal, 13 as having impaired fasting glycaemia (IFG) and 5 as having diabetes mellitus (DM). By IEC (HbA1c) criteria, 89 subjects were classified as normal, 21 as pre-diabetes and 7 as DM. By ADA (HbA1c) criteria, 69 subjects were classified as normal, 41 as pre-diabetes and 7 as DM. Alkaline phosphatase was significantly higher in hyperglycaemic states compared with normal subjects, with ANOVA F statistics of 9.45 for WHO (p < 0.001), 9.24 for IEC (p < 0.001), and 6.87 for ADA (p < 0.01). Although the numbers were small, more obese patients were categorised as hyperglycaemic (pre-diabetes and diabetes) when HbA1c-based criteria were applied, compared with WHO (glucose-based) criteria. Further studies are required to confirm this preliminary observation.