I’ve been using the Abbott Freestyle Libre Continuous Glucose Monitor (CGM) for about 9 days now and I’ve had the opportunity to compare its blood glucose measurements with the Livongo stick meter that I’ve used for a couple of years now.
The following graphs show the comparison of blood glucose measurements between the Freestyle Libre and Livongo meters.
I have several brands of stick meters that I routinely compare and there is always a delta of at least 10-20 mg/dL so I’m not surprised that these two meters don’t measure the exact same blood glucose levels. Blood glucose meter accuracy is about 20% so even multiple measurements with the same meter won’t line up exactly and can vary by 20%.
A blood glucose meter is no different than other meters that measure things like temperature, pressure, flow rates, etc. There is an accuracy stated for the meter but that accuracy may not hold true for the entire range that the meter can measure. Usually the meter manufacturer will have a tighter accuracy in a range where the measurement is more important (for example, with temperature it would be in the middle of the range where the temperature control system would expect to control). While I can’t find this information in the literature for blood glucose meters, I’d expect the accuracy of these meters to be tighter at measurements <75 mg/dL because low blood glucose level can kill you quickly.
So while I’m not surprised that the Freestyle Libre and Livongo meters have deltas in their measurements, I am surprised that the delta between the Freestyle Libre and Livongo is always positive. I would expect some to be positive and some to be negative (as the natural variation in measurement accuracies play out) but the fact that 12 of the 13 comparisons were positive (1 comparison had a delta of 0) leads me to assume that one of these meters has a consistent offset.
Now it should be stated that I have no idea which meter is closest to my actual blood glucose levels but that really doesn’t matter as long as the deltas continue to be consistent. With frequent blood glucose monitoring, the absolute value of these measurements isn’t what’s important; what you should be looking for is trends in the measurements that can be correlated with a diet or lifestyle change.
As I stated in an earlier post, I intentionally went off my typical Paleo diet for the first week of using the CGM so I could see what my blood glucose levels were after non-Paleo meals but next week I’ll return to my normal Paleo diet and I will be interested in seeing if the delta between these two meters decreases as more of my measurements are <100 mg/dL. If my theory about blood glucose meter accuracies being tighter at the lower range is true, this should play out in the data as my blood glucose levels drop to those lower ranges.
Very interesting. It doesn’t surprise me. I have been using the Abbott Freestyle Libre for 6 weeks and I test my blood glucose level a few times a day with a finger stick. I use the Freestyle neo test strips and the internal meter built into the Libre. I found very consistently that the blood glucose levels were typically 18-23 mg/dl lower than the meter/sensor reading (Interstitial glucose level). I don’t test as much now as I did at the start, because I have a very good idea of where my actual BG level runs once I take a sensor measurement. It is remarkably consistent. I have type II diabetes with a HgA1c of 10.9% two months ago and through the Freestyle Libre, it has allowed me to see what happens with a significantly modified diet. I can watch and control in real-time. I am now down to a HgA1c around 5.8 and lost 27 lbs.
That is a remarkable improvement Breck! I love to hear success stories like this. Getting this kind of instant feedback to lifestyle/diet inputs can only happen with the CGM.
Thank you both for the research and for your example. And for reminding me that the gadget that matters is not the meter or the test strip. The gadget that matters is the bicycle. I am going to get dressed and get on mine now.