Dear Dani, Grace and Jude.
Note: This page is advice for Grace, Jude and John. For any other reader, it’s information only. No therapeutic relationship is formed – read this.
CGM is a true game-changer.
A CGM device is the most important bit of the diabetes management kit. I am sure I will have got you one, if not, give my head a wobble!
This picture shows the difference between CGM interstitial glucose and finger prick blood glucose measurements.
- The CGM reading is about 5 minutes behind the blood glucose reading, so they will hardly ever match exactly.
- The CGM continually reads the glucose and updates the display every 5 minutes or so.
- The CGM tracks the direction of glucose travel and lets you know where it is heading. The arrow/s allow you to see into the future to stop highs and prevent lows. Each CGM has a different arrow system but they give the same information. They tell you where the glucose will be in 10 minutes time. Grace and Jude, if we move to America we will be using mg/dL, and 1.0mmol/L = 18mg/dL. But to keep it simple:
- 2.0mmol/L = 40mg/dL
- 1.5mmol/L = 30mg/dL
- 1.0mmol/L = 20mg/dL
CGM’s have come a long way. Back in 2010, I used one from Medtronic. The sensor was inserted by what can only be described as a javelin masquerading as an insertion needle! The sensor only lasted three days and the accuracy was dog crap! The blood and CGM values were often more than 3.0mmol/L (55mg/dl) apart. Hence needing to calibrate the sensor four times a day and confirm highs and lows with finger pricks.
However, I loved it. It was the best of its generation and it helped me to understand where my glucose went twenty-four hours a day.
I really need to show gratitude to Medtronic. Medtronic has pushed this space over the last twenty years. Without Medtronic’s investment, the CGM field would still be in the stone age. I worked for Medtronic for five years and know how passionate they are about closing the loop. Thank you, Medtronic.
How accurate are the CGM devices today?
Most of the CGM devices today meet the basic accuracy required to replace finger picks. This table shows the accuracy level required and what differences in measurements you should expect.
However, I want the best for you two, so I have investigated further. I conducted a very deep dive into the accuracy of CGM devices in the research paper I was the lead author on. You can read about it in the research part of Dynamic Glucose Management. The paper concluded there is a gold standard of accuracy for CGM devices – the FDA’s iCGM criteria.
To get iCGM approval, a CGM device must be very accurate in the low, in target and high range. Also, there must be virtually no readings that are wildly inaccurate. Only two CGM’s can boast iCGM approval, the Libre 2 and Dexcom G6 (April 2021).
I think they are both great, but I use the Dexcom G6 for these reasons:
- It tells you when there is an Urgent Low Soon, alongside having a low and high alert. The Libre 2 only has a low and high alert. This makes preventing hypos much easier with the Dexcom G6.
- There is an option to calibrate the system if the CGM reading is inaccurate. The Libre 2 does not have this option. You want to be able to course-correct an inaccurate CGM reading to prevent annoying incorrect low alerts all night.
- You see the data in real-time, the Libre 2 requires a scan.
- The Dexcom G6 has a double arrow up and down which lets you know when it’s rapidly rising and falling. The Libre 2 only has one arrow so its not possible to know the difference between rising and rapidly rising.
- Finally, I trialled them head to head over 10 days. The Dexcom G6 was more accurate, FOR ME
Why is CGM so much better than finger pricks?
There are three main reasons:
- The more feedback you have, the quicker you learn.
- High and low alerts act like barriers at the bowling alley, they keep you from falling over the edge.
- Arrows allow you to predict the future and use Dynamic Glucose Management to stay in target.
How much time in range (4.0-10.0mmol/L or 70-180mg/dL) should I aim for?
This table shows the higher the percentage of time your glucose is in range, the better your daily energy and future health. However, the amount of time spent managing diabetes goes up as time in range increases. It’s a balancing act that should fluctuate as you grow up.
In the early years, mummy and I will use Dynamic Glucose Management to get to at least 85% time in range. When you hit your teens, keeping above 70% is very manageable using Dynamic Glucose Management more loosely. Then as you become an adult, the World is your oyster.
You may even want to join the elite, with 99% time in range, by fully implementing Dynamic Glucose Management – I can only hope!
What’s next? Basal Insulin
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