Predicting the risk for CVD (cardiovascular disease) events is improved by measuring the diabetes patient’s HbA1c (hemoglobulin1c) levels, researchers from Brigham and Women’s Hospital, Boston reported in Archives of Internal Medicine.

The authors explained that diabetes is a risk factor for cardiovascular disease. However, according to recent studies, the risk varies considerably among patients with diabetes.

They wrote:

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

Nina P. Paynter, Ph.D. and team set out to determine how useful monitoring HbA1c levels might be in in predicting cardiovascular events. A HbA1c test reflects average blood glucose over the previous 8 to 13 weeks. It is generally viewed as an indicator on how well the patient is managing/controlling his/her diabetes.

The researchers gathered data from the Women’s Health Study as well as the Physician’s Health Study II. Out of 24,674 females, 685 had diabetes at baseline, while out of 11,280 males 563 had diabetes at baseline. Participants had completed questionnaires on their medical history. Baseline blood samples were evaluated for HbA1c, C-reactive protein, and cholesterol levels.

The females were followed up for new CVD incidents for an average of 10.2 years, and the males for 11.8 years.

During the follow-up periods there were:

  • Females – 125 cardiovascular events out of 685 participants. Compared to 665 out of 24,674 without diabetes.
  • Males – 170 cardiovascular events out of 563 participants. Compared to 1,382 out of 11.280 without diabetes.

The researchers wrote that including HbA1c modeling for CVD improved CVD prediction compared to the general prediction of all high risk diabetes participants. This was especially the case among females.

The risk modeling that the researchers used showed that 71.9% of women with diabetes in this study had a lower than 20% risk of CVD over a ten-year period, compared to just 24.5% of their male counterparts.

However, in the models that included a term for HbA1c, the risk prediction for a CVD improved substantially for women and more modestly for men.

The authors wrote:

“Using a yes/no term for diabetes instead of HbA1c also improved prediction over classification as high risk in both men and women. In women, however, HbA1c further improved prediction over the yes/no term.

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 authors suggest that the difference in risk between men and women is partly due to a higher risk of CVD with age, and the delayed risk in females.

They added that further studies are required to confirm their findings.

Even so, the researchers concluded:

“Our findings suggest that the improvement in CVD risk prediction, and possibly calibration, obtained with adding HbA1c levels is highest in lower-risk populations.”

Dr. Mark J. Pletcher, M.P.H., from the University of California, San Francisco, explains that cardiovascular disease guidelines, including Adult Treatment Panel III (ATP III) guidelines will soon be updated.

He wrote:

“One specific guideline refinement up for consideration this year is the approach to CVD risk stratification in patients with diabetes.”

Diabetes is seen as a “Coronary heart disease (CHD) risk equivalent” under the current ATP III guidelines. Diabetes patients may be subject to fairly aggressive goals for bringing down cholesterol levels, as well as treatment thresholds.

Dr. Fletcher wrote:

“The article by Paynter and colleagues, which includes the HbA1c level as well as other standard risk factors, appears to improve discrimination and may lead to “more accurate classification of individuals into risk categories.”

A study with more diabetes patients, especially those whose condition was not well controlled, would have provided stronger results, he added.

Dr. Fletcher wrote:

“If it had not included revascularizations and strokes, as these were not considered when the current ATP III CHD risk-prediction equation was developed and calibrated; and if the model had included a diabetes indicator variable as well as the HbA1c measurement..

..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.”

Arch Intern Med. Published July 25, 2011. doi:10.1001/archinternmed.2011.351

Written by Christian Nordqvist