The relevance of glycosylated haemoglobin in screening for non–insulin dependent diabetes mellitus in a black South African population
Background Due to population growth, aging, urbanisation, increasing prevalence of obesity and physical inactivity, diabetes mellitus (DM) has become one of the most important and prevalent chronic diseases. Glycated haemoglobin A1c (HbA1c) assessment is currently being used all over to monitor glycaemic control as a cornerstone of diabetes care. It might also be a useful screening tool for non–insulin dependent DM, also known as type 2 DM (T2DM). Elevated HbA1c can be linked with long–term risk of cardiovascular complications. Aim The aim of the study was to determine whether HbA1c can be used as reliable screening tool for early detection of T2DM in an African population. Methods This study was a cross–sectional study and was part of the South African, North–West Province (SANWP) leg of the 12–year Prospective Urban and Rural Epidemiological (PURE) study. Baseline data was collected from March to December 2005. A total of 2010 volunteers were recruited from randomly selected households. Data was collected on socio–demographic characteristics, physical activity, dietary intakes, blood pressure and anthropometry. HbA1c, fasting plasma glucose (FPG), liver enzymes and HIV status were determined. Ethical approval for the PURE study was obtained in July 2004. Oral glucose tolerance tests (OGTT) were also done for a sub–group of 465 subjects. The Statistical Consultation Services of the North–West University were consulted to analyse data with SPSS 17.0 and STATISTICA 9.0. Results The HbA1c values within the diabetic FPG groups were 7.46% for men and 8.08% for women. HbA1c values increased significantly progressively from the normal FPG groups to the groups with impaired FPG and the diabetic FPG groups for both men and women. No significant increases were found in HbA1c between the OGTT groups (normal 2 hour plasma glucose (PG), impaired 2–hour PG and diabetic 2–hour PG). Total cholesterol, triglycerides, body mass index and FPG increased significantly and high–density lipoprotein cholesterol decreased significantly with an increase in HbA1c values in men and women. In addition, systolic blood pressure increased significantly in women with increased HbA1c. Thus, with an increase in HbA1c, an increase in the number of risk factors was observed. When using HbA1c and FPG in combination, 43 subjects of the whole population were detected with having a risk of developing T2DM. However, when considering the commonality of subjects identified to be diabetic or at risk by the OGTT, FPG and HbA1c individually, only one subject was identified by all the methods as having diabetes or being at risk to develop diabetes. Discussion and conclusions An increase in HbA1c and FPG was associated with an increase in risk factors and therefore with metabolic syndrome (MS). MS is associated with an increased risk of developing T2DM and therefore it can be concluded that HbA1c was useful for detecting in this population individuals at increased risk of developing T2DM. The use of FPG and HbA1c in combination was considered a better screening tool when compared to HbA1c alone. Factors other than what were measured in this study might be the cause of the unexpected results obtained in the participants with impaired OGTT.
- Health Sciences