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From Madison, Wisconsin, USA:

I am baffled by the American Diabetes Association Clinical Practice Recommendation, one that is oft cited by the Ask the Diabetes Team members, that an A1c (or glycosylated hemoglobin) should be less than 1% above the upper limit of normal for the lab performing the test. For example, the upper normal limit of the lab that performs my A1c is 6.2%. One percent of 6.2 is.062, so 1% above the upper normal limit for this lab would be approximately 6.26 or 6.3. This doesn't provide much wiggle room above the upper normal limit. Ten percent above the normal limit, which in this case would be roughly 6.8%, seems a more reasonable goal. Am I misunderstanding the recommendation or how to calculate it?


The actual quote from the ADA is:

...treatment regimens that reduced average A1C to [about] 7% ([about] 1% above the upper limits of normal) were associated with fewer long-term, microvascular complications; however, intensive control has been found to increase risk of hypoglycemia and weight gain. Epidemiological analyses suggest that there is no threshold or lower limit of A1C above normal levels at which further lowering has no benefit. An average A1C [greater than] 8% is associated with a higher risk of complications, at least in patients with reasonably long life expectancies. The relative benefit of achieving an A1C of 7% is documented in randomized controlled clinical trials with relative risk reductions of 15-30% per 1% absolute reduction in A1C...

Although the wording the ADA uses is muddy, it does indicate that the idea of "one percent" refers to "1% absolute reduction" in the A1c value. So, if the upper limit of normal in the lab were 6%, as implied in the ADA's example, then "one percent" higher than normal would be an A1c of 7%, and "two percent" higher would be a value of 8%. That is, or course, entirely different from taking one percent of the value of 6.2% (0.062) and adding it to the 6.2% and coming up with 6.262%, as you did.

Therefore, in your lab, adding "one percent" to the upper limit of normal of 6.2% would result in the number 7.2% -- so I'd interpret the ADA's advice to be to keep your A1c at 7.2% or lower.


Additional comments from Dr. Stuart Brink:

These are tight goals and often not achievable with current medical and nutrition management. However, we know from the DCCT that a clear goal might be less than 7.5% and, if this can be achieved safely and without excessive hypoglycemia, then perhaps even 7%. Many folks with typeá2 diabetes can achieve tighter glucose control without fears of hypoglycemia, of course.

For some perspective in children around the world, the Hvidore studies demonstrate the enormous range from excellent control to horrific control. I would suspect that the United States generally falls into the mid-range of the Hvidore studies with some individual diabetes centers achieving results comparable to the DCCT even with haphazard United States insurance rules and regulations. Any comparisons must utilize a DCCT hemoglobin A1c standard assay.

Our own clinic average ran 7.4% in 2001, but we believe in a philosophy of intensified multidose insulin or insulin pump therapy with frequent blood glucose monitoring, carbohydrate counting and coverage of food/snack changes and frequent ambulatory visits as a way to achieve such overall control.


Original posting 8 Mar 2002
Posted to A1c, Glycohemoglobin, HgbA1c and Tight Control


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Last Updated: Tuesday April 06, 2010 15:09:30
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