Impaired glucose tolerance at 1 hour may be more predictive than at 2 hours, study finds

The results highlight the potential benefit of targeting individuals with an elevated one-hour blood glucose level and, if supported by additional evidence, eventually replacing the two-hour test with a one-hour measure, the authors said.

Elevated blood glucose levels in men one hour after an oral glucose tolerance test appear to better predict development of type 2 diabetes than elevated glucose levels at two hours, a recent study found.

The study included a population-based cohort of 4,867 Swedish men (median age, 48 years) who were randomly selected from prespecified birth cohorts between 1921 and 1949 as part of the Malmö Preventive Project. Participants underwent oral glucose tolerance testing and had blood glucose measurements taken at zero, one, and two hours. Over a median of 33 years of follow-up, researchers used registry data to determine diabetes diagnoses and other outcomes. They then compared elevated glucose levels at one hour (defined as ≥8.6 mmol/L [154.8 mg/dL]) versus at two hours (≥7.8 mmol/L [140.4 mg/dL]) in terms of ability to predict incident diabetes, vascular complications, and mortality. Results were published online on Nov. 14 by Diabetes Care.

During the follow-up period, 636 participants (13%) developed diabetes. Compared to elevated two-hour glucose levels, elevated one-hour glucose levels were significantly associated with incident diabetes (hazard ratio, 3.40; 95% CI, 2.90 to 3.98; P<0.001) and provided better risk assessment (C index, 0.637 vs. 0.511; P<0.001). When patients were stratified by fasting glucose, adding the one-hour measurement provided greater net reclassification improvement than adding the two-hour measurement (0.214 vs. 0.016, respectively). Elevated glucose levels at one hour were also significantly associated with mortality, myocardial infarction or fatal ischemic heart disease, retinopathy, and peripheral vascular complications compared to normal levels. Glucose levels that were normal at one hour and elevated at two hours were not associated with any increased risk.

The study authors noted limitations, such as changes in the definition of type 2 diabetes over the study period and the cohort's intake of a 30 g/m2 glucose load, rather than the standard 75 g/m2 load. The generalizability of the results to patients other than white men may also be limited, they added.

“Our results highlight the potential benefit of targeting individuals with an elevated 1-h blood glucose level and provide a strong rationale for an interventional study in which subjects are selected based on this abnormality,” the authors wrote. “Should preventive efforts prove beneficial in this relatively large group, it would become prudent to consider 1-h blood glucose as a replacement for 2-h blood glucose” as the preferred marker of impaired glucose tolerance.