HbA1c and mortality: What are the risks?

This study explored the association between HbA1c (an average measure of blood glucose [sugar] over 3 months) and mortality in patients with prediabetes and diabetes.

HbA1c levels are a tested marker for long-term blood glucose levels and diabetes. HbA1c levels greater than 6.5% generally lead to a diagnosis of diabetes, and HbA1c levels between 5.7% and 6.5% are considered prediabetic. HbA1c has also been associated with increased risks of other disorders. Both men and women see an increase in cardiovascular disease (including heart attack and stroke) with higher HbA1c levels, while women see an increase in risk of cancer and death from that cancer. However, whether or not HbA1c is associated with mortality (death) in those with or without diabetes is not clear.

This study explored the records of 22,106 patients with and without diabetes to examine the association between HbA1c and mortality risk from all causes, cancer, and cardiovascular disease. Of the total patients, 1,019 were diagnosed as diabetic (732 with uncontrolled [high] blood glucose, 53 with controlled blood glucose, and 234 with moderately high blood glucose). 413 patients had elevated HbA1c levels but had not been diagnosed with diabetes prior to the study. 5,198 had prediabetes but had not been diagnosed prior to the study. Patients were followed for 7 years. By the end of the follow-up period, 1,509 patients had died: 506 of cardiovascular disease and 466 of cancer.

All-cause mortality was increased by 85% in patients with uncontrolled diabetes (diabetes diagnosis plus HbA1c >6.5%) compared to those without diabetes. Those with undiagnosed (no diabetes diagnosis but HbA1c >6.5%) or moderately high HbA1c levels (diabetes diagnosis plus HbA1c between 5.7 – 6.5%) also saw a 40% increase in risk, but those with prediabetes (no diabetes diagnosis but HbA1c between 5.7-6.5%) did not see an increase. Women with uncontrolled diabetes had 2.27 times the risk of mortality than did patients without diabetes, and women with undiagnosed diabetes had a 61% increase. Men with uncontrolled diabetes had a 62% increase in risk.

Each group of patients had an increased risk of death from cardiovascular disease compared to those without diabetes, from an 89% increase in risk for those with moderately raised HbA1c levels to more than 3 times the risk for those with controlled diabetes. Men with controlled diabetes, in particular, had 4.55 times the risk of death from cardiovascular disease compared to men without diabetes; for women with controlled diabetes that risk was 90% higher. No significant increase in risk were seen for patients with prediabetes.

There was no significant increase in risk of death from cancer in any of the groups.  

This study concluded that there was an association between HbA1c levels and mortality, particularly death from cardiovascular disease.