are all current continuous glucose blood monitor sensors the same tech?

June 9, 2020 5:07 PM

Like it says on the box. : ) Are they?

I just had a crazy incident I won't go into here with some Libre sensors; all this is new to me, I was just advised to try it for a couple weeks to get some baseline data since I've been feeling weird; no prior diabetes diagnosis. Doc says I must be one of the 15% of skinny outliers who don't have enough subcutaneous fat for them to register the data properly; all of the 1.5 weeks of data it took was variably wack. Similar readings from other sensors in batch. We know this because fingerstick and arm blood draws confirmed they were way off, at several times during the same day. Doc also says all the currently available ones use the same sensing tech, so switching brands, likely pointless. ?

posted by bitterkitten to Health & Fitness (6 answers total)

In our household we've used Libre for a couple of years, and recently Dexcom for a couple of months. The Libre was useful to a point, but Dexcom are way more accurate (Libre lagged behind fingerstick readings and was often off by a couple of mmol/L). I don't know how the tech they use differs, but there is a big difference in how accurate they are.
posted by EndsOfInvention at 5:30 PM on June 9, 2020

Agreed Dexcom is more accurate. I wore one of each for awhile to test it. But I don’t know if it’d be any better for you in particular, given the doctor’s opinion.

Are you open to wearing it elsewhere? The pectoral area is sometimes used by people who have trouble with arms and stomach. As long as the data is good, it doesn’t hurt and it doesn’t fall off, you’re good!
posted by michaelh at 7:11 PM on June 9, 2020

Mr. Gryphonlover is thin and uses a dexcom G6 on his upper arm. Works perfectly.
posted by gryphonlover at 8:18 PM on June 9, 2020

Libre lagged behind fingerstick readings and was often off by a couple of mmol/L

This is expected behaviour for any CGM, because all of them monitor interstitial fluid rather than actual blood, and interstitial fluid glucose levels are not always the same as blood glucose levels.

Glucose moves between blood and interstitial fluid by diffusion rather than active transport, so there needs to be a difference between BGL and IFGL for that to happen and it takes a while to equalize. This is why an IFGL-monitoring CGM will generally lag behind finger stick readings.

But cells remove glucose from IF using an insulin-mediated active transport, so when insulin levels are high you'll quite often see far lower readings from an IFGL sensor than from a BGL sensor like a finger stick glucometer. This is also why an IFGL sensor can actually give timely warnings of an oncoming hypo, since the only time a hypo is going to develop quickly is when there is a lot of insulin on board.

We didn't run our Dexcom sensor for long enough to get much familiarity with it because it was annoyingly and intrusively lumpy, but I'd be astonished if these two effects didn't also happen with those.

Libre sensors are quite temperature-sensitive; they will regularly read up to 2mmol/l higher than reality during and soon after a hot shower, for example.

And every now and then they "drop out" for half an hour at a stretch, yielding readings well under what a finger stick test shows for none of the above reasons. I'm guessing this has something to do with physical disturbance to the sensor but haven't been able to confirm for sure; I suspect that whatever does this is probably also what makes them inaccurate if they're applied to a patch of skin without much subcutaneous fat.

I don't have enough experience with Dexcom sensors to know to what extent they're similar in these respects.
posted by flabdablet at 9:11 PM on June 9, 2020

I found this to be helpful in understanding the 'how' behind how they work. I know there are significant differences between the algorithms the 'brains' part (your phone or their receiver) uses to interpret the raw data, and then there are 'add' on programs (spike, xdrip etc) which can further tinker with that data. There are also differences in the chemistry and physical technology between sensors as well.

Using the freestyle Libre there are options to take the data and use the add on program to do more with the data. We use a 'Miao Miao' transmitter to capture the data from the libre and view it with Nightscout, and although this setup is not without it's problems, it does seem to provide more stable and useful data to us. Consider carefully what the end goal of the CGM is: Better picture of trends? Avoid undetected hypoglycemia? Easier sharing of data with providers. If you want to PM about Libre Sensors, we have a lot of experience with them, and I'm happy to share our experiences and the tricks we have learned. There is 100% a learning curve to the Libre's quirkiness, but overall it's been a game changer in this household!
posted by Northbysomewhatcrazy at 2:23 PM on June 10, 2020 [3 favorites]

Response by poster: thx for the tips. If it turns out i definitely need them, I will experiment again, because stabbing myself in the fingers all the time, much as it is starting to overcome my fear of blood etc, seems really inefficient.
posted by bitterkitten at 6:10 PM on June 11, 2020