We read with interest the consensus statement of the American Diabetes Association on postprandial blood glucose published in the April 2001 issue of Diabetes Care (1). We are concerned about the following consensus position in that report regarding the relation among postprandial glucose (PPG), fasting plasma glucose (FPG), and HbA1c: “In summary, there are insufficient data to determine accurately the relative contribution of the FPG and PPG to HbA1c. It appears that FPG is somewhat better than PPG in predicting HbA1c, especially in type 2 diabetes.” Absolute FPG is not a reliable tool for management of type 2 diabetes. Trovati et al. (2) evaluated whether a fasting blood glucose <6.7 mmol/l can predict overall blood glucose control in 287 type 2 diabetic patients. They found that 56% of the subjects had PPG values >8.9 mmol/l or <4.4 mmol/l, and that HbA1c was not correlated with fasting blood glucose concentrations. Conversely, the same authors pointed out that fasting hyperglycemia does not exclude the occurrence of low glucose values throughout the day in both diet-treated and drug-treated type 2 diabetic patients (3). Thus, FPG alone is not predictive enough of the overall control in type 2 diabetes.
Bouma et al. (4) showed in 1,020 type 2 diabetic patients that HbA1c is difficult to predict from FPG values: only 66% of the patients with HbA1c <7.0% were identified by FPG values <7.8 mmol/l. HbA1c is difficult to predict from FPG values, and predicting HbA1c changes from FPG changes is even more difficult. Finally, Avignon et al. (5) demonstrated in 66 type 2 diabetic patients that postlunch (2:00 p.m.) and extended postlunch (5:00 p.m.) plasma glucose (PG) correlated significantly and independently with HbA1c, but that prebreakfast PG and prelunch PG did not. Moreover, postlunch PG and extended postlunch PG demonstrated better sensitivity, specificity, and positive predictive value in predicting poor glycemic control than prebreakfast PG or prelunch PG. In summary, published data don’t support the conclusion that FPG is somewhat better than PPG in predicting HbA1c, especially in type 2 diabetes.
We think that in a period in which the idea of evidence-based medicine is maturing and is better defined, one shouldn’t undervalue the results of these studies (some of which were published in this journal), which were conducted with a large number of patients.
Address correspondence and reprint requests to Giovanni Ghirlanda MD, Inst. Internal Medicine and Geriatrics, Catholic University, L.go Gemelli 8, 00168, Rome, Italy. E-mail: email@example.com.