It’s taken me a while to accept this reality. I feel clinicians who adopt the unthinking rule of thumb that any A1c under 6.0% automatically means excessive hypoglycemia. This is not always true.
One simple metric that doctors (and patients) can use to analyze hypo vulnerability in patients who use a CGM is to examine blood glucose variability as measured by standard deviation. The higher the standard deviation (SD), the higher glucose variability.
Here’s an example. Let’s say a patient receives the news of a 5.9% A1c from her/his doctor and and their CGM data reveals a standard deviation of 70 mg/dL (3.9). That A1c equates to an average blood glucose of 123 mg/dL (6.8). A standard deviation of 70 (3.9) means that roughly two thirds of all their data points fall within one standard deviation on either side of their average. In this case that means 123 +/- 70 or a range of 53 to 193 (2.9 to 10.7).
Contrast that with another patient who also has an A1c of 5.9% but whose CGM standard deviation is 30 mg/dL (1.7). That means that approximately 2/3 of their blood glucose falls with a range of 123 +/- 30 or 93 to 153 (5.2 to 8.5). As you can see the risk of hypos is dramatically reduced with this lower SD. In fact, this patient could target lowering their BG average without increasing hypo risk!
What I’m trying to say here is that a reasonable BG average as indicated by an A1c measurement is not the full story. It’s when a reasonably in-range BG is combined with large variability that is the real culprit.
Variability as measured by standard deviation should be the focus of the doctor/patient treatment discussion. Concentrating on the A1c number alone is not helpful and misses an opportunity to really help the patient. In some cases I see this short-sighted analysis as lazy. And it insults the clinician’s best performing patients!
If you want a lower A1c yet also don’t want to increase your risk of hypos then concentrate on BG variability first and average BG second.