Regardless of diabetes diagnosis, glycated hemoglobin (HbA1c) levels are associated with mortality, with risk for all-cause mortality increasing with HbA1c levels that are too low or too high, according to results published in The Journal of Clinical Endocrinology & Metabolism.

The true associations between HbA1c and survival are still being debated, as there has not been conclusive evidence for optimal HbA1c ranges among various populations. To evaluate the range of HbA1c levels associated with all-cause mortality in patients with and without diabetes, researchers conducted a study of participants from the Health and Retirement Study who had available HbA1c data and no history of cancer (n = 15,869). The researchers used Cox proportional hazards regression models to estimate hazard ratios with 95% CIs for mortality.

Participants had a median age of 64 years. During a median follow-up of 5.8 years, 2133 participants died.

For participants with diabetes, those with an HbA1c level of 6.5% had the lowest risk for all-cause mortality. Participants with HbA1c <5.6% or >7.4% had significantly increased risk for all-cause mortality compared with those with HbA1c of 6.5%.

For participants without diabetes, those with an HbA1c level of 5.4% had the lowest risk for all-cause mortality. Participants with HbA1c <5.0% had significantly increased risk for all-cause mortality compared with those with HbA1c of 5.4%. The researchers did not find a statistically significant increase in all-cause mortality risk for participants without diabetes who had HbA1c >5.4%.

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Based on this evidence, the researchers stated that for patients with diabetes, the optimal HbA1c level range is 5.6% to 7.4%, while for those without diabetes, it is 5.0% to 6.5%.

“Our findings suggested a U-shaped and a reverse J-shaped association for all-cause mortality among participants with and without diabetes,” the researchers wrote.

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Reference

Li FR, Zhang XR, Zhong WF, et al. Glycated hemoglobin and all-cause and cause-specific mortality among adults with and without diabetes [published online March 21, 2019]. J Clin Endocrinol Metab. doi:10.1210/jc.2018-02536