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Lower Cutoff for Impaired Fasting Glucose Identifies Those Without High CVD Risk

Risk of CVD mortality among people with IFG largely explained by conversion to diabetes. New research found that the current cutoff for impaired fasting glucose set by the American Diabetes Association identifies a group of people who do not have elevated risk of cardiovascular disease. Only those individuals who convert from impaired fasting glucose to diabetes have a higher risk for mortality.

In 1997, the ADA introduced a cutoff value to diagnose IFG. In 2003, this value was lowered from  110mg/dL or 6.1 mmol/L (IFG6.1) to 100mg/dL or 5.6 mmol/L (IFG5.6).

Josina M. Rijkelijkhuizen, PhD, of the Institute for Research in Extramural Medicine at the VU University Medical Center in Amsterdam, and colleagues conducted a study assessing the effect of lowering the IFG cutoff on the prevalence of IFG and on the associated risk of all-cause and CVD mortality. They also examined whether the link between IFG and mortality is independent of the conversion to diabetes. The study cohort consisted of 1,428 individuals who took part in the Hoorn Study, which began in 1989 in the Netherlands. There was a mean follow-up period of 6.4 years, and patients were followed with respect to mortality.

The prevalence of IFG5.6 at baseline was 33.2% vs. 10.1% for IFG6.1. The mean fasting plasma glucose level of the entire cohort was 100mg/dL or  5.6 mmol/L in 1989 and 112mg/dL or 6.2 mmol/L in 1996; thus, the prevalence of IFG5.6 increased to 55.7% while the prevalence of IFG6.1 increased to 25.6%.

Among those individuals with IFG6.1 in 1989, 42% progressed to diabetes over the course of the study, and the incidence rate was 66.5/1,000 person-years. In contrast, only 21% of the IFG5.6 patients developed diabetes, with an incidence rate of 32.7/1,000 person-years..

During the period from the physical examination in 1996 until Jan. 1, 2005, 192 individuals died; 81 were determined to have died from CVD. For those with IFG6.1, the HR for CVD mortality was 1.87 relative to the reference group with normal glucose levels.

“The HR for CVD mortality for the IFG5.6 group was lower and not statistically significant: 1.37 (95% CI, 0.87-2.16),” the investigators wrote. The two IFG groups both had significantly higher risk for CVD mortality compared with the normal group.

Further analysis showed that individuals with either IFG5.6 or IFG6.1 who did not convert to diabetes did not have significantly higher risk than individuals who had normal fasting glucose levels and did not convert to diabetes.

“Subjects with IFG5.6 or IFG6.1 status who had converted to diabetes during the 6.4 years of follow-up had higher all-cause and CVD mortality risks than subjects who were classified as newly discovered diabetes in 1989 and had significantly (up to 2.5 times) higher all-cause and CVD mortality risks than subjects with normal glucose status at that time,” the investigators wrote.

“The fact that CVD mortality risk is only present in those subjects who will develop diabetes within six years indicates that our focus should lie on treatment of CVD risk factors and early detection of diabetes,” they wrote. Rijkelijkhuizen JM, Nijpels G, Heine RJ, et al. High risk of cardiovascular mortality in individuals with impaired fasting glucose is explained by conversion to diabetes.

Diabetes Care. 2007;30:332-336.

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