What is a Dexcom CGM compression low? Why does it happen?

There is always a moment of panic when we see a compression low on his iPhone receiver. It is usually a sudden drop and it is never a good feeling to wake up to an alert sound paired with a “LOW” reading on the CGM. We immediately do a finger poke to check his blood glucose number. That usually assures us that us was just a “compression low”. When we first started using a CGM, we thought it was happening because we only put it on his arms but when we started using other sites on his body, we ran into the same inconsistencies.

Dexcom Sugarmate Image of a compression low (false low)

So what is a compression low really?

A compression low is not a true reading of a person’s blood glucose (BG) levels. It usually occurs when the body is pressing on the transmitter and sensor site while asleep (you are sleeping on it). The sensor will read much lower than the glucose meter and the drop trajectory will appear sudden and rapid on your device. 

Why does it happen?

The CGM (Dexcom in our case) does not really measure blood glucose, it reads how much glucose is in the interstitial fluid (IF) through the sensor wire inserted under the skin. When the body is pressing on the sensor, the interstitial fluid gets spread out (squished) and the sensor does not get an accurate reading. To get a more accurate reading of BG, a finger poke is always the way to go.  

It is worth mentioning that it is important to recognize a compression low (false low) from a true low to avoid over treating with carbs or going through an unnecessary recalibration of the CGM. 

What to do?

It may sound too easy but moving the weight of the body off of the CGM will help the readings go back on track. My son is usually in deep sleep when our compression lows happen. We just help flip him on his other side to remove the pressure from the CGM site. Again, a finger poke is the first action to take to make sure it is not a true emergency low. Dexcom has not addressed compression lows in their FAQ page to date.

compression low SS T1D sugaremate

Note: I am not a medical professional, please consult your medical team for your health questions and contact your CGM company if you have device specific questions.

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