Background: The aim of this study was to estimate the progression rates from normal glucose tolerance (NGT) to impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and diabetes, and from IFG and IGT to diabetes in first-degree relatives (FDRs) of individuals with type 2 diabetes mellitus.

Methods: A total of 701 non-diabetic FDRs of consecutive patients with type 2 diabetes aged 20-70 years in 2003-2005 were followed through 2007 for the occurrence of IGT, IFG and type 2 diabetes. Glucose tolerance classification was based on the criteria of the American Diabetes Association and standard 75 g 2-h oral glucose tolerance test (OGTT).

Results: The progression rate from NGT to IFG, IGT and diabetes were 8.6% (95% confidence interval (CI) 6.8-10.6), 3.7% (95% CI: 2.5-5.1) and 0.5% (95% CI: 0.1-1.2) per year after an average of 27.6 months, respectively. Progression rates from IFG and IGT to diabetes were 5.1% (95% CI: 2.1-10.2) and 9.9% (95% CI: 7.7-12.6) per year.

Conclusions: To our knowledge, these are the first estimate of progression rates from NGT to IFG, IGT and diabetes in FDRs of individuals with type 2 diabetes in Iran. The progression rates to diabetes in these participants are high, and intensive follow-up and intervention strategies are recommended for these high-risk individuals.

Keywords: first-degree relatives; diabetes mellitus; impaired glucose tolerance; impaired fasting glucose; impaired glucose regulation; progression rate