Relationship between A1C and glucose levels in the general Dutch population: the new Hoorn study

Abstract

Objective: To investigate the relationship among A1C, fasting plasma glucose (FPG), and 2-h postload plasma glucose in the Dutch general population and to evaluate the results of using A1C for screening and diagnosis of diabetes.

Research design and methods: In 2006-2007, 2,753 participants of the New Hoorn Study, aged 40-65 years, who were randomly selected from the population of Hoorn, the Netherlands, underwent an oral glucose tolerance test (OGTT). Glucose status (normal glucose metabolism [NGM], intermediate hyperglycemia, newly diagnosed diabetes, and known diabetes) was defined by the 2006 World Health Organization criteria. Spearman correlations were used to investigate the agreement between markers of hyperglycemia, and a receiver operating characteristic (ROC) curve was calculated to evaluate the use of A1C to identify newly diagnosed diabetes.

Results: In the total population, the correlations between fasting plasma glucose and A1C and between 2-h postload plasma glucose and A1C were 0.46 and 0.33, respectively. In patients with known diabetes, these correlations were 0.71 and 0.79. An A1C level of > or =5.8%, representing 12% of the population, had the highest combination of sensitivity (72%) and specificity (91%) for identifying newly diagnosed diabetes. This cutoff point would identify 72% of the patients with newly diagnosed diabetes and include 30% of the individuals with intermediate hyperglycemia.

Conclusions: In patients with known diabetes, correlations between glucose and A1C are strong; however, moderate correlations were found in the general population. In addition, based on the diagnostic properties of A1C defined by ROC curve analysis, the advantage of A1C compared with OGTT for the diagnosis of diabetes is limited.

Figure 1

Scatter plots of FPG and 2-h postload plasma glucose in relation to A1C in the total population. Diabetic patients are indicated by dotted reference lines at FPG levels of 7.0 mmol/l and 2-h postload plasma glucose levels of 11.1 mmol/l.

Figure 2

ROC curve for identification of participants with previously undiagnosed diabetes, using A1C for diagnosis and an OGTT as criterion. A1C cutoff points of 5.8, 6.0, 6.5, and 7.0% are indicated on the curve.