I’m starting to have a bit of a love hate relationship with my Libre. I love the trend information. It makes the whole process of basal testing and understanding how your body works so much easier and allows you to understand what to do to make changes in a way that blood testing simply can’t do.
I hate the inconsistent accuracy of the thing. In the last 24 hours I’ve seen variation from blood tests that have been between 5.5% and 17.5%, and that’s with my glucose levels in the range 5.4 to 6.7.
After starting yesterday within the normal 5% or so range, it just stopped being accurate. As I’m adjusting basal at the moment, my blood glucose did rise over the course of the day, but the velocity wasn’t fast nor the rise high. It peaked at around 9 mmol/l and was managed back down. This seemed to cause the Libre no end of trouble and once I started coming back down again, it didn’t want to follow. As you might imagine this was highly frustrating. To cut a long story short, the sensor appeared to be misbehaving.
Before bed, this is what the numbers looked like across both sensors. Each was 17.5% out, just one up and one down, in a normal blood glucose range:
Now, overnight, I’ve had a nice flat and steady graph. I went to bed with a blood glucose of 5.8 and awoke with a 5.4. My blood sugar point readings showed 5.7 at the point of checking with my basal, while my interstitial showed as 6.7 (yes that is 17.5% away). Over the course of the next hour the interstitial level dropped back to 6.1 while my blood levels didn’t change, and remained reasonably constant throughout the night. On waking, bloods showed 5.4 while the interstitial was 5.9. This morning’s view is this:
Again, what seems to be going on here is yet another variation in either what the sensor is seeing or what the reader is interpreting from the sensor. Otherwise, where did the blip on the old sensor/reader combination come from? Another slightly odd discrepancy.
As there were plenty of blood tests done yesterday, it will be an interesting exercise to pull the data off the device and put together a graph showing the variance of the new sensor and the old sensor. I wonder what the standard deviation from the blood glucose recordings will be?
Yesterday’s experience also makes me wonder about the rate at which interstitial fluid glucose levels change in relation to those of the blood, and more importantly, which one matters?
If my IFG is 10 and my BG is 8, which is better? I assume my IFG should be <8 as well? What are the mechanisms I have to get my IFG lower, other than running my BG at a lower level and waiting for it to catch up? If my IFG is higher than my BG, what happens to the tissues? Does a high level of protein in my diet cause the IFG to “stick” at a higher level and change more slowly?
There are many questions to answer and it’s not always clear where the answers are or what they should be. So the inconsistencies seem to be two things. Different data collection points and difference reactions to the available carbohydrate. The joys of being a guinea pig!