Libre HbA1c v Actual HbA1c

[mashedupmatt]

Changed my latest sensor an hour or so ago after phoning Abbott (9 days in ; Libre 2+) - it said that I had basically been hypo for the last 24 hours, but was actually approximately 5 mmol/L different (higher) on a finger prick- changed it once they said that they would send another one, but now have signal loss error - oh the joys....

 

[PerSpinasAdAstra]

I am not convinced that calibrating CGMs is a great advantage because of the error margin on BG meters and the difference between one make of BG meter and another and I generally find that Libre consistently predicts only 2-3 mmols lower than my actual result, which is pretty impressive in my opinion over 4 years worth of 6 monthly testing. Especially if you consider that there is likely an error factor of 1 or 2mmols on an HbA1c result. I don't know that for sure but it seems reasonable.

Calibrating isn't always a good idea certainly. A lot depends on the quality of the meter. Some meters are very much better than others. I've been testing this in the last few months - so far I've done around 700 tests from the same drop of blood with more than one meter at a time, up to five meters per test, with ten meter models in total, while wearing CGMs to see how the readings compare. For me the Libre 2 nearly always reads high and my actual HbA1c tests have always been quite a bit lower than my Libre 2 GMI numbers. Others seem to have different results though - I can't explain it. My favourite theory right now is that the depth of the layer of fat under the patch of skin where the sensor is applied, or perhaps factors such as how much water a person typically drinks, might be influencing the automatic calibration. Just a guess though - these are the only things I can think of which might vary significantly between individuals which might produce consistently high or low readings from sensor to sensor.

In a few months I'll gather all the reading into spreadsheets, generate some plots and try to do some statistical analysis. I have to wait until warmer weather to finish the testing though, to be sure that higher room temperatures don't affect the differences I'm seeing between meter models. What I can say though is that a Dexcom One+ calibrated with a Contour Next or Contour Next One is remarkably consistent. Calibrate it right and if you take a finger stick reading hours, sometimes even days later, the CGM reading will often come within 0.1 or 0.2 mmol/L a few minutes after the blood reading. For me at least that's very much closer to the mark than I've ever seen with my Libre 2s. That said, I'm certain that using some of the other meters I have would be a mess - impossible to calibrate a CGM well with them because the readings jump around so much from test to test. Hopefully I'll be able to rank the meters, if I can learn the maths on how to do that - verify the best of the premium meters and the best of the four meters I have that use cheap test strips. Hopefully.

 

[goodybags]

I’ve only had a Hba1c done once since I started using Libra just over 6 months ago
but the result was 48 and if I recall correctly the Libra predicted it as 46 (currently Libra prediction is 45) so will see what my result is in April when I will be getting my next Hba1c done
But for me the Libra has been a big help

Strangely Libra estimates Hba1c is still predicted as 45, same as when I previously posted back in January

have just booked my next appointment with the Vampire for the 16th
what we going to go with … 😉

Higher
or
Lower

 

[silver minion]

Strangely Libra estimates Hba1c is still predicted as 45, same as when I previously posted back in January

have just booked my next appointment with the Vampire for the 16th
what we going to go with … 😉

Higher
or
Lower

Lower I reckon. Maybe 43?

 

[goodybags]

Bloods taken yesterday, Hba1c result is 46
Libra forecast was 45

so that’s pretty good (both the actual result & the Libra forecast)

 

[Phil P]

Late reply to this but my Libreview estimated HbAC1 is reporting that it is using 90 days of data as per the attached s/shot.

and for info it was reporting 35 mmol/mol when my last HbAC1 was measured from blood sample at my GP (37 mmol/mol). Strangely, this seems more accurate than the absolute values reported against finger prick test (and I do compensate for the 15 min difference) where I am usually around 2-3 mmol/L higher by finger prick. I am self-funding on the Libre 2 Plus as I am Type 2 and my main reason for using it is to see how well I keep in range and how fast the readings drop after a spike - so more interested in the shape of the daily graph than the actual values.