Libre CGM and ambient temperature?

[Greyman]

Has anyone else noticed a sharp increase in libre CGM readings when the ambient temperature falls or that their sensor tends to read higher than finger-prick tests or their actual A1C test results?

For example, when I get up in a morning, particularly during the colder months, my sensor reading rises dramatically. This isn't a removing-pressure-on-the-sensor thing, by the way, as this rise also happens when I go outside the house, into a cooler temperature.

This might not be the only factor, but my estimated A1C results have been 7-8mmol/mol higher, when compared to my actual A1C results. Also, the finger-prick tests I have done to check when these apparent dramatic rises occur, tend to be way lower and more in line with my actual A1C results. This isn't just a case of the delay between blood and interstitial fluid levels.

The difference has become pretty predictable, so I can get a good idea of what my actual A1C is likely to be, but I am just curious as to whether anyone else might be experiencing something similar?

The Libre2+ is apparently the same as the previously used Libre2 by the way.

I have not seen any other comments of similar behaviour elsewhere, so I'm starting to wonder if it's just my body that has a weird chemical reaction when it gets cold. I do tend to prefer to be on the cold side of comfortable. 🙂

 

[rebrascora]

The rise on a morning is what we call Foot on the Floor which is a slightly more sociable version of Dawn Phenomenon. I always inject my breakfast bolus as soon as I wake up and always before I get out of bed to combat it. If I am not having breakfast depending upon what my waking reading is, I inject 1.5-2units of bolus insulin to deal with it.
It isn't Libre playing up but a genuine rise due to the liver releasing glucose to give you the energy to go out and hunt or forage for your first meal of the day. Our bodies haven't yet caught on that we have developed kitchen cupboards and fridges and supermarkets, so we don't need the same surge of glucose that our prehistoric ancestors did to run down a wooly mammoth for breakfast.

As regards Libre giving results which are consistently higher or indeed lower than actual results, I believe this comes down to body chemistry. For me Libre is consistently lower than finger pricks and my HbA1c is usually a few mmols higher than it's prediction although my last one was spot on with my actual result.

In my opinion it is still a really great, life changing bit of kit and as the discrepancy is usually reasonably predictable and consistent, I can accept this as one of it's foibles even though it but it does show me as being in the red quite a bit more than advised no more than 4%. It used to bother me that it messed up my stats and looked like I was having more hypos than I actually was but my consultant is really happy with my results, so I don't let it get to me anymore.

 

[Greyman]

The rise on a morning is what we call Foot on the Floor which is a slightly more sociable version of Dawn Phenomenon. I always inject my breakfast bolus as soon as I wake up and always before I get out of bed to combat it. If I am not having breakfast depending upon what my waking reading is, I inject 1.5-2units of bolus insulin to deal with it.
It isn't Libre playing up but a genuine rise due to the liver releasing glucose to give you the energy to go out and hunt or forage for your first meal of the day. Our bodies haven't yet caught on that we have developed kitchen cupboards and fridges and supermarkets, so we don't need the same surge of glucose that our prehistoric ancestors did to run down a wooly mammoth for breakfast.

As regards Libre giving results which are consistently higher or indeed lower than actual results, I believe this comes down to body chemistry. For me Libre is consistently lower than finger pricks and my HbA1c is usually a few mmols higher than it's prediction although my last one was spot on with my actual result.

In my opinion it is still a really great, life changing bit of kit and as the discrepancy is usually reasonably predictable and consistent, I can accept this as one of it's foibles even though it but it does show me as being in the red quite a bit more than advised no more than 4%. It used to bother me that it messed up my stats and looked like I was having more hypos than I actually was but my consultant is really happy with my results, so I don't let it get to me anymore.

I love my CGM too and perhaps too much, as I did initially get into a habit of spending more time watching it than getting on with life. I initially got an A1C of 34mmol/mol, but that prompted more "hypos" and, perhaps more importantly led to a fair bit of weight gain. I think I've got a better balance now though, being happy with around 39mmol/mol although a recent sensor falling off and leaving me with just one, did panic me a little, at the prospect of being without. Thankfully, Abbott are really fast at turning round replacements.

The elevated readings I'm experiencing aren't just around the time that dawn phenomenon would hit and I can and have actually been able to deliberately move the sensor reading, by going out into the cold, putting on clothes or taking them off. Sorry for any images that might have conjured. 🙂

 

[helli]

I haven't spotted this discrepancy but one thing I notice every morning with any CGM I use (I have used 5 different ones over the years) is when I have a shower it always reports a spike.
As this is a real spike (up when I get under the hot water and down about 10 minutes after I get out) without any insulin to cause it to come down, I believe it is something to do with the heat in the shower.

 

[rebrascora]

But foot on the floor doesn't happen at the same time as DP. It happens when you get out of bed and start walking around and lasts about 45 mins for me if I don't treat it. I actually discovered it before getting Libre by doing lots of finger prick testing and my levels would rise by as much as 6mmols in that 45 mins after getting up and before I had breakfast. Doing exercise the night before can significantly reduce it though but that is because my muscles recoup their glucose stores whilst I sleep, so I have to reduce my evening basal dose (Levemir being shorter acting allows me to do this) to prevent nocturnal hypos.

Ambient temperature affects insulin sensitivity but may also affect subcutaneous fluid composition as does dehydration of course, so going out in the cold and taking clothes off or putting them on could affect your interstitial fluid readings compared to blood which is maintained at a more stable level, so yes there can be circumstances where Libre gives more significantly different readings to blood.

If I have been doing a lot of really physical activity like trimming horses hooves on a hot day and not drinking enough, then my Libre will read higher than my actual levels and when I then come home and have a drink, my levels suddenly drop because that fluid is then rehydrating me and diluting the glucose in my subcutaneous fluid.

 

[Greyman]

I haven't spotted this discrepancy but one thing I notice every morning with any CGM I use (I have used 5 different ones over the years) is when I have a shower it always reports a spike.
As this is a real spike (up when I get under the hot water and down about 10 minutes after I get out) without any insulin to cause it to come down, I believe it is something to do with the heat in the shower.

That would appear to be the opposite of what I am experiencing, as higher ambient temperature causes my sensor to read lower, so maybe the heat of the water on the outside of your sensor is having an effect?

I'll check that out when I next shower, but I'll need to be careful, as this warm, sweaty weather does seem to reduce the sensor's grip on my skin.

 

[Greyman]

But foot on the floor doesn't happen at the same time as DP. It happens when you get out of bed and start walking around and lasts about 45 mins for me if I don't treat it. I actually discovered it before getting Libre by doing lots of finger prick testing and my levels would rise by as much as 6mmols in that 45 mins after getting up and before I had breakfast. Doing exercise the night before can significantly reduce it though but that is because my muscles recoup their glucose stores whilst I sleep, so I have to reduce my evening basal dose (Levemir being shorter acting allows me to do this) to prevent nocturnal hypos.

Ambient temperature affects insulin sensitivity but may also affect subcutaneous fluid composition as does dehydration of course, so going out in the cold and taking clothes off or putting them on could affect your interstitial fluid readings compared to blood which is maintained at a more stable level, so yes there can be circumstances where Libre gives more significantly different readings to blood.

If I have been doing a lot of really physical activity like trimming horses hooves on a hot day and not drinking enough, then my Libre will read higher than my actual levels and when I then come home and have a drink, my levels suddenly drop because that fluid is then rehydrating me and diluting the glucose in my subcutaneous fluid.

I'd not actually heard of this "foot on the floor" thing, but the finger-prick test I still do before injecting before meals, shows that the sensor is reading way higher.

It's that change in interstitial fluid composition where I think my experience might be based.