Libre 2 v Finger Prick test

[Laz]

Hi, just fitted my first Libre 2 sensor, taken 3 finger prick readings and each finger prick test is 2-3 mmol lower than the Libre sensor, any reason why ? Is this normal ??

Many thanks

 

[helli]

There are a few things to consider which are described in this thread https://forum.diabetes.org.uk/boards/threads/cgm-limitations-and-precautions.108188/
The other thing to consider is that all meters need to comply with a standard of being within 15% of the "real" value. If your BG is higher than 9, it is very possible for the two readings to be more than 2mmol/l different if your finger prick meter is reading 15% low and your Libre is reading 15% high.

 

[John Gray]

@Laz My results are almost the opposite to yours: my Libre 2 readings are 1-2 mmol/L higher than finger-prick readings!
I've just started on the newer Libre 2 Plus sensor - and hope that this gives somewhat more 'together' readings.
@helli states the appropriate mathematical similarity.

 

[Standup]

My Libre also tends to be 2-3 mmol higher than the finger prick especially when high. I tend to use it for trends rather than absolute numbers (and to wake me in the night if it goes too low).

I think some of the other readers you can calibrate but I've not seen anything about doing it on the Libre.

 

[rebrascora]

In range (3.9-10) my Libre usually and fairly consistently reads about 1mmol lower than a finger prick, but if levels are rising sharply or above 10 then Libre will usually be higher and over exaggerate any peaks, just like it over exaggerates any lows.

I tend not to do a comparison test between Libre and a finger prick unless there is no active food or insulin in my system and my levels have been reasonable stable and mid range (5s and 6s) for half an hour as that is when they are most comparable. If they are within 2 mols in that scenario then they are good enough for me to calculate my insulin doses from or corrections throughout the range, but it is very rare that they are more than 1mmol lower in that situation. If it is consistently more than 2mmols out then it gets reported and Abbott will replace it.

 

[helli]

Bear in mind, if your Libre readings are consistently higher or lower than finger pricks, it could be your finger prick meter that is higher/lower, especially if the discrepancy is the same for multiple sensors.

 

[SimonP]

I think some of the other readers you can calibrate but I've not seen anything about doing it on the Libre.

You can with something like XDrip+

Bear in mind, if your Libre readings are consistently higher or lower than finger pricks, it could be your finger prick meter that is higher/lower, especially if the discrepancy is the same for multiple sensors.

Does this hold true for readers or just batches of strips. I wonder how much this actually happens vs libre calibrations being off.

One way to test this is to use calibration fluids for the blood tester, not sure I have any mind you!

 

[everydayupsanddowns]

You may find it settles over the next 48-72 hours @Laz

But if the readings from this sensor remain substantially adrift from your meter readings, do give Abbott a call, who will troubleshoot the sensor with you, and may well replace it of they consider it isn’t performing as expected.

Remember to keep well hydrated too - sensors read the fluid in around cells in tissue, and hydration helps that ‘interstitial’ fluid to flow properly 🙂