CGM: When is it NOT reliable?
I’ll be the first one to say it; CGM is the greatest invention for PWD since insulin. By providing real-time and predicative information, it has allowed us PWD to take control of our DM management. I honestly don’t know how I every functioned without it. It is the key to success in diabetes. We talk a lot about how and when to use CGM, but equally as important is learning when NOT to use it.
One of the most common mistakes that I see happen with PWD on CGM involves over-correction of low blood sugar. Remember, CGM is measuring subcutaneous fluid, NOT blood glucose. Because of this, CGM data often lags behind blood glucose during rapid rates of change (like after correcting a low).
Picture this scenario; Amy was fast asleep when she got a CGM alert for low blood glucose. She looked at her CGM which read 60mg/dl. She took 15 grams of fast-acting carbs and waited 15 minutes; just like she was instructed by her endo. Fifteen minutes later, she looked at her CGM which read 65mg/dl. WHAT?! She took 15 more grams of fast-acting carbs and 30 minutes later her BG was over 200mg/dl. What happened?
Chances are, her blood glucose was rising after her first 15-gram carb intake, but the glucose hadn’t yet reached her subcutaneous fluid. It was therefore not yet detected by her CGM. If she had done a fingerstick prior to her second correction, she would have likely seen that her blood glucose was much higher than her CGM reading. She likely didn’t need that second 15-gram carb correction.
Though everyone is different in what they need to correct low BGs, I ALWAYS recommend using fingerstick/blood glucose when correcting and during rapid rates of change. This way, PWD are much more likely to avoid overcorrecting lows and hopping on the subsequent roller-coaster that most of us are all too familiar with.
Also, this is my nephew on Halloween and I’m pretty sure he’s the cutest kid in the entire world.
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