Does HbA1C predict isolated impaired fasting glycaemia in the oral glucose tolerance test in subjects with impaired fasting glycaemia?

BACKGROUND: To assess the usefulness of erythrocyte glycated haemoglobin (HbA1C) as a screening tool to identify those subjects with impaired fasting glycaemia (IFG) who do not have impaired glucose tolerance (IGT) or diabetes mellitus (DM) on a 75 g oral glucose tolerance test (OGTT). Design and methods All subjects undergoing an OGTT had HbA1C measured at baseline. Receiver operator characteristics analysis was used to identify optimal HbA1C cut-off values for diagnosing and excluding IGT and DM. RESULTS: We studied 140 subjects (69 women) with IFG (fasting capillary plasma glucose between 6.1-6.9 mmol/L). Using World Health Organisation criteria, 27 had isolated IFG, 56 had IGT and 57 had DM. HbA1C was higher (P < 0.001) in patients with DM (6.8 +/- 0.93%) when compared with those with IGT (6.3 +/- 0.68%) and isolated IFG (6.2 +/- 0.30%), but HbA1C was similar in those with IGT and isolated IFG. There was no HbA1C cut-off value differentiating isolated IFG from IGT or DM. None of the subjects with isolated IFG had HbA1C concentration of >6.8%, but 76% and 54% subjects with IGT and DM, respectively, had HbA1C of < or =6.8%. CONCLUSIONS: HbA1C measurement is of limited value in differentiating isolated IFG, IGT and DM in subjects with IFG. It cannot be used to identify which subjects with IFG do not require an OGTT.

Screening for Addison's disease in patients with type 1 diabetes mellitus and recurrent hypoglycaemia.

BACKGROUND: Addison's disease may present with recurrent hypoglycaemia in subjects with type 1 diabetes mellitus. There are no data, however, on the prevalence of Addison's disease presenting with recurrent hypoglycaemia in patients with diabetes mellitus. METHODS: Three year retrospective study of diabetic patients with "unexplained" recurrent hypoglycaemia investigated with a short Synacthen test to exclude adrenocortical insufficiency. RESULTS: 95 patients with type 1 diabetes mellitus were studied. Addison's disease was identified as the cause of recurrent hypoglycaemia in one patient with type 1 diabetes mellitus. CONCLUSION: Addison's disease is a relatively rare but remedial cause of recurrent hypoglycaemia in patients with type 1 diabetes mellitus. A low threshold for investigating patients with type 1 diabetes mellitus and recurrent hypoglycaemia to detect Addison's disease is therefore suggested.

Ethnic differences in glycated haemoglobin between white subjects and those of South Asian origin with normal glucose tolerance.

OBJECTIVE: To determine whether ethnic differences exist in glycated haemoglobin between white subjects and those of South Asian origin with normal glucose tolerance (NGT) METHODS: Erythrocyte glycated haemoglobin (HbA(1c)) was compared between white subjects and those of South Asian origin with NGT defined by a 75 g oral glucose tolerance test (OGTT). RESULTS: 139 subjects with NGT comprising 36 people of South Asian origin (20 female) and 103 white subjects (49 female) were compared. Subjects of South Asian origin were younger (p<0.001) and weighed less (p<0.001) than white subjects. Fasting and 2 h capillary plasma glucose concentrations were similar in subjects of South Asian origin and white subjects, but HbA(1c) levels were higher (p<0.05) in subjects of South Asian origin (6.11+/-0.58%) compared with levels in white subjects (5.90+/-0.40%). CONCLUSION: In subjects with similar fasting and postprandial glycaemia on OGTT, those of South Asian origin have higher HbA(1c) levels than white subjects. It is speculated that the higher glycaemia-independent HBA(1c) levels in people of South Asian origin could possibly contribute to their increase cardiovascular risk.