AIM: Testing HbA1c levels in diabetics can improve CVD risk prediction

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Evaluating hemoglobin A1c levels in diabetic patients can help improve the risk prediction for cardiovascular disease, according to a study published online July 25 in the Archives of Internal Medicine. These results may lead to a more accurate diagnosis for patients in certain risk categories.

“It is unclear whether models that include hemoglobin A1c [HbA1c] levels only for diabetic patients improve the ability to predict cardiovascular disease [CVD] risk compared with the currently recommended classification of diabetes as a cardiovascular risk equivalent,” Nina P. Paynter, PhD, from Brigham and Women’s Hospital in Boston, and colleagues wrote.

To better understand HbA1c levels for diabetic patients, Paynter et al evaluated data from the Women’s Health Study and the Physician’s Health Study II to analyze the predictive value of HbA1c levels, which tests average blood glucose levels.

The study used data from 24,674 women (685 with diabetes at baseline) and 11,280 men (563 had diabetes at baseline). Patients filled out questionnaires answering questions about medical history, and blood samples were taken to evaluate cholesterol, C-reactive proteins and HbA1c levels. Women were followed up for an average of 10.2 years and men were followed for an average of 11.8 years.

“Simulated cost-benefit analyses have suggested that this variability in CVD risk could provide an opportunity for tailored preventive therapy in diabetic patients,” Paynter and colleagues wrote.

Paynter et al reported 125 cardiovascular events in the 685 women with diabetes and 170 CV events in the 563 men with diabetes.

In a risk model, the authors found that 71.9 percent of female diabetic patients had a less than 20 percent risk of CVD over a 10-year period compared to only 24.5 percent of male diabetic participants with a predicted 10-year CVD risk of less than 20 percent.

Models that included a term for HbA1c improved the CVD risk prediction for women, but there was a more modest improvement in risk prediction for men. “Using a yes/no term for diabetes instead of HbA1c also improved prediction over classification as high risk in both men and women,” the authors wrote.

HbA1c improved prediction over the yes/no term in women, the authors found.

“We found that in these large population-based cohorts of both men and women, presence of diabetes alone did not confer a 10-year risk of CVD higher than 20 percent, and measurement of HbA1c level in diabetic subjects improved risk prediction compared with classification as cardiovascular risk equivalent,” the researchers wrote.

Paynter and colleagues speculated that the difference in risk between the sexes could be due to the increase in CVD risk with age and the delayed risk in women.

“Our findings suggest that the improvement in CVD risk prediction, and possibly calibration, obtained with adding HbA1c levels is highest in lower-risk populations,” the authors concluded. “In both women and men with diabetes at baseline, we observed significant improvements in predictive ability of CVD risk using models incorporating HbA1c levels compared with classification of diabetes as a cardiovascular risk equivalent.”

In an accompanying editorial, Mark J. Pletcher, MD, MPH, from the University of California, San Francisco, said that the current data may lead to a more accurate classification of patients into certain risk categories.

However, Pletcher offered that the results could have been stronger if more diabetic patients were included, especially those whose condition was not well controlled.

Reclassifying some patients with diabetes to lower risk levels could disqualify them from statin therapy to reduce cholesterol levels. “It is not enough to know whether discrimination or reclassification improves with the additional measurement; harm from the new measurement strategy (both direct and indirect) must be considered and weighed against a realistic estimate of the expected health benefits,” Pletcher concluded.