Do you know your Hemoglobin A1C?
Hemoglobin A1C: Do you know your level?
You may be at increased risk for diabetes and heart disease and not know it. There’s a blood test that turns out to be an accurate measure of risk for both of these common diseases. Until now it was pretty much ignored unless you already had diabetes.
Hemoglobin A1C(HgA1C) — also called glycated hemoglobin — is a commonly ordered test for diabetics. It measures how many red blood cells carry extra glucose molecules; it is used to calculate average blood sugar levels over a 3 month period.
Abnormally elevated levels of HgA1C are associated with diabetes. Poorly controlled diabetes is associated with a level above 8.0%. There’s a great deal more to the story.
It turns out that high normal levels of HgA1C in people without diabetes or heart disease are highly accurate measures of the risk of both. This is important because it gives us information that can trigger the sort of diet and lifestyle measures that help prevent either of these diseases.
HgA1C was measured in 11, 092 adults who did not already have diabetes or heart disease. They were part of the Atheroslcerotic Risk in Communities (ARIC) study and ther measurements were made in the 1990 – 1992 period. Subsequent progression to diabetes and heart disease was recorded when it occured. Study subjects were followed up until January 1, 2006, for an average of approximately 15 years.
So-called hazard ratios were calculated for various ranges of HgA1C. The hazard ratio is the increased risk of developing the disease at some time in the future, compared to a normal baseline. For example, a HgA1C between 6.0 and 6.5% puts you at a 4.48 times greater risk of developing diabetes over a 15 year period than a HgA1C of 5.0 to 5.5.
Up until now, fasting blood sugar has been used to diagnose diabetes. A level between 100 and 125 mg/dL is referred to as pre-diabetic; when fasting glucose rises to above 125 mg/dL, this is diabetes. Fasting levels are taken after skipping food for at least 8 hours.
Given a baseline HgA1c of 5.0 to 5.5%, the incremental increased risks of diabetes are: 5.5 to 6.0 % — 1.86 times normal; 6.0 to 6.5% — 4.48 times normal; 6.5% or greater — 16.47 times normal. Over the same ranges of HgA1C, the increased risk of heart disease range from 1.23 to 1.95 times normal.
HgA1C gives doctors and patients alike useful information for clarifying risk of both diabetes and heart disease. Hopefully it will prove more useful than fasting blood glucose levels in motivating people to take their health into their own hands.
In the meantime, know your HgA1C.
Data taken from Glycated Hemoglobin, Diabetes, and Cardiovascular Risk in Nondiabetic Adults, Selvin and others, New England Journal of Medicine, March 4, 2010