Postchallenge Glucose, HbA1c, and Fasting Glucose as Predictors of Type 2 Diabetes and Cardiovascular Disease: A 10-year Prospective Cohort Study

doi:10.2337/dc10-0262

Postchallenge Glucose, HbA_1c, and Fasting Glucose as Predictors of Type 2 Diabetes and Cardiovascular Disease: A 10-year Prospective Cohort Study

Henna Cederberg, MD (henna.cederberg{at}oulu.fi)^a,
Tuula Saukkonen, MD^a,^b,
Mauri Laakso, MD^a,^c,
Jari Jokelainen, MSc^a,^c,
Pirjo Härkönen, MNSc^d,
Markku Timonen, MD, PhD^a,
Sirkka Keinänen-Kiukaanniemi, MD, PhD^a,^c,^e and
Ulla Rajala, MD, PhD^a

^a Institute of Health Sciences, Faculty of Medicine, University of Oulu, Finland
^b Oulu Occupational Health Centre, Hallituskatu, Oulu, Finland
^c Unit of General Practice, Oulu University Hospital, Oulu, Finland
^d Oulu Deaconess Institute/Diapolis Oy Research Unit, Oulu, Finland
^e Oulu Health Center, Diabetes Unit, Saaristonkatu, Oulu, Finland

Abstract

Objective HbA_1c has been proposed as a new indicator for high risk of type 2 diabetes. The long-term predictive power and comparability of elevated HbA_1c with the currently used high risk indicators remain unclear. We assessed HbA_1c, impaired glucose tolerance (IGT) and impaired fasting glucose (IFG) as predictors of type 2 diabetes and cardiovascular disease (CVD) at 10 years.

Research Design and Methods Prospective population-based study of 593 inhabitants from northern Finland, born in 1935, was conducted between 1996 and 2008. Oral glucose tolerance test (OGTT) was conducted at baseline and follow-up and HbA_1c determined at baseline. Those with a history of diabetes were excluded from the study. Elevated HbA_1c was defined as 5.7-6.4%. Incident type 2 diabetes was confirmed by two OGTTs. Cardiovascular outcome was measured as incident CVD or CVD mortality. Multivariate log-binomial regression models were used to predict diabetes, CVD and CVD mortality at 10 years. Receiver operating characteristic curves compared predictive values of HbA_1c, IGT and IFG.

Results Incidence of diabetes during the follow-up was 17.1%. Two in three of the newly diagnosed diabetes was predicted by a raise in one or more of the markers. Elevated HbA_1c, IGT or IFG preceded diabetes in 32.8%, 40.6% and 21.9%, respectively. CVD was predicted by intermediate and diabetic range of 2-h glucose, but only by diabetic HbA_1c levels, in women.

Conclusions HbA_1c predicted 10-year risk of type 2 diabetes at range of 5.7-6.4%, but cardiovascular disease only in women, and at range ≥6.5%.