Guidelines for Diabetes Control Challenged
New Research Has Experts Rethinking How Low A1c Should Be
Sep 17, 2008
Scott, 70 years old, suspected that his new doctor gave him bad advice. His old doctor had said to try to get his average blood sugar, A1c, below six. Now, the new doctor said “seven is fine.” Scott wondered if the new doctor, while younger, was actually a little behind the times.
Probably not. The “best” A1c level for an individual depends on many factors, and should result from discussion between the patient and clinician. Some recent research may help explain the new doctor’s advice for Scott.
ACCORD Study
Researchers enrolled more than 10,000 North American adults with Type 2 diabetes. The treatment goal was to get their A1c level lower than six using intensive treatment (more medication, more frequent testing). The control group was treated in the usual way, generally with an A1c target of seven. Researchers expected the intensive treatment group to have fewer cardiovascular (heart and blood vessel) events. To their surprise, though, the opposite was true. In fact, the study was stopped 18 months early because the intensive treatment group actually had more cardiovascular events, such as heart attacks and strokes.
Three and a half years later, the differences had evened out—overall there was no cardiovascular event difference between the two groups. The intensive treatment group had fewer non-fatal heart attacks, but more fatal heart attacks.
What is A1c?
A1c is a short label for hemoglobin A1c, also called HbA1c. A1c is hemoglobin containing glucose, a sugar. It’s a marker of average blood glucose over the past four to six weeks. It’s a simple enough test: a blood sample is taken, the hemoglobin A1c is isolated and measured as a percent of total hemoglobin.
How A1c Reflects Average Blood Glucose
Hemoglobin is in red blood cells, which are constantly being destroyed and replaced. Glucose is packed into the new cells according to the concentration of glucose in the bloodstream, making more or less A1c. Some days, a lot of A1c is made, other days, much less. As the new and old red cells mix, the amount of A1c is enhanced or diluted. Overall, the relative amount of A1c represents average blood glucose. Some experts say the A1c is weighted more by blood glucose levels in the previous two weeks.
Other Studies
Another study, the ADVANCE Trial, had over 11,000 subject from 20 different countries. The subjects selected already had a history of some cardiovascular problem. Again, the target A1c for the study group was less than 6.5%. In this study, the intensive treatment group had less blood vessel damage to their kidneys. But there was no difference in heart attacks and strokes.
A third recent study, VADT, had 1,800 US veterans. Researchers expected intensive treatment would reduce cardiovascular events. At the start, the average A1c was 9.5 (moderately high). After treatment, the average had dropped to 6.9% in the intensive treatment group, and 8.4 in the standard treatment group. After six years, their was no difference in cardiovascular events between the two groups.
So Why Try to Lower A1c So Much?
Other studies have shown that each reduction of A1c by 0.7% lowers the rate of cardiovascular events by one sixth. Some suggest that the problem with the ACCORD study was that the A1c was lowered too rapidly. Others point out that there is a difference between older people who only recently developed diabetes and those who had it for many years. In the studies described here, the averages ages were 62, 66, and 60 years. Older people may be more susceptible to possible low blood sugar with intensive treatment. Younger patients may benefit heavily by intensive treatment by reducing their risk of kidney and eye damage from diabetes. But for older patients, the American Geriatrics Society suggests that they may benefit from a more cautious approach, especially since the cardiovascular benefits from intensive treatment, that is, a treatment A1c goal of less than 6.5%, have been challenged.
