Q: I’ve used a CGM (continuous glucose monitor) for many years. It is usually reliable, but sometimes — especially during the night — it shows a sudden sharp glucose decline out of the blue. Why does this happen?
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A: Yeah, I’ve seen those myself. The trend graph is doing just fine, and then for no reason, the glucose seems to fall off a cliff. And then a few minutes later, it corrects itself and gets back to normal. It looks like a sharp, narrow “V” shape on the trend graph. These are called “compression” lows. The glucose is not really dropping fast … the sensor just thinks it is because of physical pressure being placed directly on the sensor site. This can happen at night if you lay on the sensor while sleeping or during the day from things like seatbelts or harnesses.
The exact reason for the sensor malfunctioning under those conditions isn’t entirely understood, but it may be related to pushing interstitial fluid (the fluid in the fat layer under the skin where the sensor rests) away from the sensor for a short while. The best way to avoid compression lows is to wear the sensor on a part of the body that is less likely to receive a lot of pressure.
It is important to not overreact to compression lows since there is a good chance you are not actually experiencing a low glucose. The next time your glucose takes a sudden, inexplicable nosedive, do a finger-stick to see what the glucose really is. If it is low, treat it. If not, wait a few minutes. Chances are, the sensor will correct itself and return to normal.
Want to learn more about managing blood glucose? See our “Blood Sugar Chart,” then read “What Is a Normal Blood Sugar Level?” and “Strike the Spike II: How to Manage High Blood Glucose After Meals.”
