Normal fasting plasma glucose and risk of prediabetes and type 2 diabetes: the Isfahan Diabetes Prevention Study

Abstract

Aim: To determine the association of fasting plasma glucose (FPG) level within normal range and the risk of prediabetes and type 2 diabetes in an Iranian population.

Methods: A total of 806 first-degree relatives (FDRs) of patients with type 2 diabetes who had FPG levels less than 5.6 mmol/l (100 mg/dl) in 2003 to 2005, and who did not have diabetes or impaired fasting glucose (IFG), were followed through 2010 for the occurrence of prediabetes or type 2 diabetes. At baseline and through follow-ups, participants underwent a standard 75 g 2-hour oral glucose tolerance test (OGTT).

Results: The incidence of type 2 diabetes, impaired glucose tolerance (IGT), and IFG was 9.6 (95% confidence interval (CI): 6.8-12.4), 28.7 (23.8-33.6), and 33.0 (27.7-38.2) per 1,000 person-years based on 4,489 person-years of follow-up, respectively. FPG was associated with the incidence of diabetes, IGT, and IFG. The multivariate-adjusted hazard ratios (95% CI) for diabetes, IGT, and IFG were 1.36 (1.01-1.84), 1.45 (1.10-1.91) and 1.31 (1.00-1.71), for the highest quintile of FPG compared with the lowest quintile, respectively.

Conclusions: An increase in FPG in the normal range is associated with an increase in the incidence of IGT, IFG, and type 2 diabetes. These results prove FPG in the normal range to be useful in identifying apparently healthy FDRs of patients with type 2 diabetes at risk of developing prediabetes and diabetes.

Figure 1. Schematic diagram of the study population and course of investigation

Of the 3176 first-degree relatives (FDRs) of type 2 diabetes patients, followed between 2003 and 2010, 806 individuals fulfilled the inclusion criteria (FPG ≤ 5.6 mmol/l, absence of IFG or diabetes, age ≥ 30 yr, and at least one review in follow-up period of 5.6 yr), and were included in the study to test for diabetes development. 2370 individuals were exceluded because they did not fulfill the inclusion chriteria or because of pregnancy. 1919 of these did not have a clinical visit in follow up, 451 had FPG ≥ 100. Of the 806 included subjects, 148 developed IFG, 129 IGT, and 43 diabetes. The other 486 FDRs remained without signs of diabetes development. FPG: fasting plasma glucose. IFG: impaired fasting glucose. IGT: impaired glucose tolerance.

Figure 2

Receiver operating characteristic (ROC) curves for normal fasting plasma glucose for prediction of IGT, IFG, and type 2 diabetes in first-degree relatives of type 2 diabetes patients, with baseline FPG levels <5.6 mmol/l. The estimates of the area under the ROC curves and their 95% confidence intervals are shown in Table 4.