Using CGM trend arrows
Updated: Mar 18, 2020
Most people who start continuous glucose monitoring therapy love it. Why? Because it provides real-time AND predictive information about our blood sugars. Knowing how to make use of this information is the key to success with a CGM. So today I want to talk about CGM trend arrows and how to use them.
What is the therapeutic difference between a CGM reading of 220mg/dl with two arrows up, and a CGM reading of 220mg/dl with two arrows down? For me, it is a difference of taking a 5.25U correction or a 0.75U correction dose.
Let me explain. According to the above chart published in Endocrine Society 2017 (swipe right), trend arrows are best used to predict the BG in 30 minutes time, and that predicted BG (not the current reading) is what should be used to calculate insulin doses.
For example, my correction factor is 1 unit for every 40mg/dl >100mg/dl.
If my CGM read 220mg/dl with two arrows pointing upwards (and I had no insulin-on-board), I would calculate a correction for a BG of 310mg/dl (220mg/dl + 90mg/dl). My correction would then be 5.25U [(310mg/dl – 100mg/dl)/ 40mg/dl].
If my CGM read 220mg/dl with two arrows pointing downwards, I would calculate a correction for a BG of 130mg/dl (220mg/dl – 90mg/dl) and would give a correction of 0.75U [(130mg/dl – 100mg/dl)/ 40mg/dl].
What a difference!
Remember, when changing the way you dose your insulin, always start conservatively and ALWAYS run your changes by your clinician first!