The new libre 2 CGM and exercise

[CBeresford]

I have noticed that a brisk walk drops my blood sugar into the red zone. I am prediabetic so not on any medication, and have not taken any action as my blood sugar comes up again as soon as I stop exercising, sometimes spiking. Last night it went down to 3.4 about 15 minutes into my walk, with this new system I was able to see its progress without scanning however I scanned at 3.4 and made an exercise note next to the logged entry. It took about 15 minutes to get back into the green, as a prediabetic should I be eating something when this happens or just leaving it to my liver sort out?, (I have had alt liver function tests in the past that were very high, though back to normal at my most recent test). Secondly when I looked at libre view it is not showing any red on the graph for yesterday despite the line clearly going below the normal range and the manual log I did when it was 3.4 has not been recorded. I have noticed with the previous system as well that my scanned logs might be well below 3.9 but is rarely classed as a hypo by libre. In fact I have only had one hypo event according to libre despite this happening every time I go for a walk. Does it only count as a hypo if it lasts longer than say 15 mins?

 

[Inka]

People without diabetes drop below 3.9 quite often. The Libre 3.9 setting is really for people on insulin and similar. If you’re not on any meds and your body raised your blood glucose back up by itself, then that’s normal. You shouldn’t need to eat as your body sorted it out as it’s supposed to.

Also, the Libre can be inaccurate at lower and higher numbers so unless you finger-pricked, you wouldn’t know what the true reading was.

 

[CBeresford]

That’s fine, I never have any symptoms and it does sort itself out.

 

[rebrascora]

It is important to understand the limitations of Libre and how it works.... Because it measures interstitial fluid instead of blood it has an inbuilt algorithm which tries to make up for this (interstitial fluid lags about 15 mins behind blood) so it uses the previous readings to extrapolate in order to predict what the current reading will be. This is fine when levels are fairly stable but when they are rising or falling quite quickly and then change direction the Libre temporarily over eggs it. Whilst you are walking, your levels will start dropping and you have a sharp downward trend but at some point your liver will start to balance that out by releasing some of it's stores. Libre doesn't detect that liver release straight away because it is in the blood stream and takes about 15 mins to get into the interstitial fluid and change the sensor readings, so the extrapolation continues to suggest that your levels are continuing to drop, when actually they have started to rise, so it will look like you are lower than you are. The daily graph is based on an average of the readings over 15 minute periods so it dampens out those "over extrapolated" peaks and troughs, so the low reading you saw doesn't sit on the graph line and your levels probably didn't dip into the red at all. Libre is just not good at dealing with those changes of direction of BG in real time, but the later graph is likely a much better reflection of what actually happened.

Sounds like your walk did exactly what you needed it to.

 

[CBeresford]

That’s great information thanks, and explains why when I look at yesterdays graph it doesn’t show a dip below 3.9. As I said my alt levels have not always been good and I was told I have a fatty liver a few years ago. I have lost weight and am a normal BMI. My HBA1c was 44 in March but is now 32, so it is all looking good. I was worried that my liver was not functioning very well (not releasing glucose quickly enough) despite the improvements to my blood glucose.

 

[Tdm]

Libre is a drama queen...it extrapolates, but then in the cold light of day, it has second thoughts and redraws the curve....you used to be able to see the spot readings from the scans which were way off the graph