HbA1C level has modest effect on predicting cardiovascular disease risk

A person’s hemoglobin A1C (HbA1C) level has a modest effect on predicting atherosclerotic cardiovascular disease risk, according to a linear regression model.

If people had an HbA1C of less than 5.7 percent, their predicted risk was reduced by 0.4 percent to 2.0 percent. If the HbA1C was 6.5 percent or higher, the predicted risk was increased by 1.0 percent to 2.5 percent. People with an HbA1C of 6.5 percent or higher had a risk that is similar to being five years older.

However, higher atherosclerotic cardiovascular disease risk did not correlate with higher HbA1C and lower risk did not correlate with lower HbA1C.

Lead researcher Jamie A. Jarmul, of the University of North Carolina, and colleagues published their results online in Circulation: Cardiovascular Quality and Outcomes on Sept. 8.

“We’re very interested in cost effectiveness modeling and trying to improve cost effectiveness modeling,” Jarmul told Cardiovascular Business. “One thing that’s really important when you’re talking about screening strategies or population-level strategies is understanding the underlying prevalence or distribution of biomarkers in the population. That’s what this work does. It builds up to doing cost effectiveness modeling.”

Jarmul said that patients with a clinical diagnosis of diabetes have an increased risk of cardiovascular disease. Although elevated HbA1C is associated with diabetes and an increased risk for cardiovascular events, the 2013 American College of Cardiology/American Heart Association Pooled Cohort Risk Equations did not incorporate HbA1C or other measurements of glycemia.

In this analysis, the researchers evaluated data and used sex, race/ethnicity and other traditional cardiovascular risk factors in the 2011 to 2012 National Health and Nutrition Examination Surveys. They were interested in understanding the expected distribution of HbA1C conditional on other cardiovascular risk factors and demographic characteristics and incorporating the information in an established risk prediction algorithm.

The final analysis included 2,000 nonpregnant people who were between 40 and 79 years old and had data available on their HbA1C, systolic blood pressure, total cholesterol, high-density lipoprotein (HDL) cholesterol, smoking and hypertension treatment status. People were excluded if they had previously been diagnosed with diabetes, congestive heart failure, coronary artery disease, angina, heart attack or stroke.

Of the people, 52 percent were women, 39.3 percent were white, 26 percent were non-Hispanic black, 20.8 percent were Hispanic and 14 percent were non-Hispanic Asian.

The linear regression model took into consideration the following variables to calculate the predicted 10-year atherosclerotic cardiovascular disease risk: age, sex, race/ethnicity, total cholesterol, HDL-cholesterol, systolic blood pressure, smoking status and hypertension treatment status.

All of those variables were significant predictors of HbA1c, according to the researchers. They defined normal HbA1C as less than 5.7 percent, pre-diabetes or borderline diabetes as 5.7 percent to 6.5 percent and diabetes as 6.5 percent or higher.

They said that people who were Hispanic, non-Hispanic black and non-Hispanic Asian had increased HbA1c compared with whites. However, their post-test atherosclerotic cardiovascular disease risk was similar to whites.

To calculate the 10-year atherosclerotic cardiovascular disease risk, they used the 2013 American College of Cardiology/American Heart Association Pooled Cohort Risk Equations.

“We didn’t expect there to be huge down classifications or up classifications in risk based on HbA1C,” Jarmul said. “A lot of patients have information about HbA1C already in their chart. It’s already been collected or it’s something that will be routinely collected at any visit. It’s really cheap and it’s not hard to do. If the information is easy to get, you have a better chance of getting value from it.”