The Increasing Importance of HbA1c for Diabetics

Diabetic people are clearly at increased risk of cardiovascular disease (which may often be fatal), compared with non-diabetics.  So, in such patients, particular attention is paid to the recognized cardiovascular risk factors: systolic blood pressure, total and low-density lipoprotein (LDL) cholesterol, smoking status, C-reactive protein (CRP), and parental history of premature heart attack.  (And, of course, diabetes is itself a risk factor in this list, allocated a likelihood of increasing the risk of cardiovascular disease increasing more than 20% over 10 years.)  In order to sharpen the predictability of cardiovascular events, Boston researchers have analyzed the potential of including the glycosylated hemoglobin (HbA1c) level as a risk factor.  The used data from two large studies, and published their findings in the Archives of Internal Medicine. 

The studies were the Women’s Health Study (WHS) and the Physician’s Health Study II (PHS II), with more than 24,000 women and 11,000 men, respectively.  Cardiovascular events (i.e. heart attack, stroke, coronary bypass or stenting, or cardiovascular death) occurred in 170 diabetic and 1,282 non-diabetic women, and in 170 diabetic and 1,382 non-diabetic men.    

Complex statistical analyses showed that, in these populations, a diabetic’s overall 10-year risk for a cardiovascular event was often lower than 20%, especially in women and young men.  If the HbA1c determination was substituted for the diagnosis of diabetes, it was possible to reclassify 19% of the diabetic women and fewer than 1% of the diabetic men to a lower risk of a cardiovascular event – actually to less than 5% risk of an event.

To quote the comment of the investigators: “These results are consistent with previously published studies suggesting that not all diabetic patients are at high

risk of future vascular events.”  Moreover, “We found improvements in prediction

in both men and women with the use of HbA1c levels in diabetic subjects compared with classification of diabetes as a cardiovascular risk equivalent.”  What’s annoying to me is that there isn’t any clear indication, anywhere in their article, of what HbA1c level is considered relevant for use in the risk analysis.  This might be useful for us patients to know!