DexcomOne+ vs Libre 2 vs Prick test

I've used the Libre2+ and whenever I've compared the Libre reading with the finger prick value there was not much in it. I know that @Rachox has had the Dexcom for a while now, so maybe she will have some ideas on that.

Thanks for the tag @IanBish . I recently switched from the Libre 2+ to Dexcom ONE +. I have found the Dexcom more accurate after a couple of calibrations (though not all sensors have required calibration being accurate from the start), something which is not possible with the Libre. Price wise the Dexcom works out cheaper if you take out the 90 day subscription. I wrote out a spread sheet comparing them so I’ll attach it here, but please if there is anything else you want to know just ask it here @Moggey

Edit, sorry just need to edit the image to make it readable! Done! That’s better

Moggey said:

thank you so much for taking the time lay that out for me

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I confess I wrote it out a while ago and posted in elsewhere on the forum. I knew it would come in useful again!

It is possible to calibrate Libre readings by using an excellent 3rd party app: Juggluco.nl

The general difficulty with such calibrations for both Dexcom and Libre is that you are calibrating to single, or a few, fingerpicks that are themselves of questionable accuracy.

Juggluco allows you to run two sensors at the same time for 12hrs on changeover. That allows you to compare around a hundred readings between old and new sensors.
New sensors do tend to be less accurate for 24-48hrs so calibration at this time is less accurate but seeing both graphs on the same display is valuable.

We often see that fingerprick tests are of similar accuracy to hospital venous blood draw, though how a single drop in a £10 meter can be as accurate as a large sample in equipment costing over £1000 evaluated by an experienced professional is in my view questionable. But let us look at the accuracy of that hospital blood test : the British Medical Journal gives a warning to Doctors about the variation in these blood tests. We can see this : it shows large variations so we must accept that any calibration using blood tests also has large variations.

Here is an example from the BMA tool.
A blood result of 7.0 can actually mean a true value of anywhere between 5.7 and 8.3. Do you really want to calibrate to such a variation?

You can compare the variations of your own readings here :

Moggey said:

Good evening all, thank you for the help I have received on beginning of my journey. My GP suggested I should get a free trial of DexcomOne + and Libre 2+ , I have done this and currently have the Dexcom on, I am finding it a great source of information as it highlights what food seem to affect me levels , one thing I have noticed is that the Dexcom and prick test seem to vary quite a bit, I get like 5.1 on the Dexcom and 7.2 on the prick test, I have calibrated the Dexcom, which should I trust ? or do I just aim for the middle 6.1 ? also what works out cheaper the Dexcom or Libre ? prices seem to vary greatly depending on which pharmacy I look at ! Many Thanks

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They say that a margin of error of 20% between Dexcom and meter is acceptable although the example you give is greater. I mostly get a maximum margin of error of 20% so am happy with Dexcom, I'm not happy with the poor quality of the machine eg too many sensor failures, not enough flexibility with the data. I expect better considering the huge cost of the sensors and the possible massive profits Dexcom are making,

Hi, hope you're all having a good day.
I've just had my medication changed (addition of 0.25ml ozempic weekly and a reduction in insuline from 20 units to 10). This is my second week on the regime. I have been using Libre for a year now and, according to my Libre my 90 day average is currently 7.7. I got a low glucose alarm yesterday showing me at 2.9 so I done a finger prick and it came up at 8.1. I stayed in the red most of the evening.

I had a Dexcom trial sitting there so I decided to put it on my other arm. The variances have totally disheartened me. One reading of Lib 3.1, Dex 11.5, Finger 12.1. Another - Lib 3.3, Dex 10.5, Finger 11.4.

I could actually cry right now because I am so confused. I though I was doing well (last A1c was 125, now, according to Libre 48). Now I don't know what to think or what to trust!

Antje77 said:

Sounds like you have a dodgy Libre. Call Abbott or fill out the form online and they'll likely send you a new one. Keep the dodgy one, they might want you to send it back.

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Hi, I was thinking that. What is bothering me though is the Dexcom readings - I've been going between 5 and 7.5 across the day according to Libre (previous sensors). I am surprised at the deviation between that and the Dexcom and the Finger prick.

Irene1902 said:

Hi, I was thinking that. What is bothering me though is the Dexcom readings - I've been going between 5 and 7.5 across the day according to Libre (previous sensors). I am surprised at the deviation between that and the Dexcom and the Finger prick.

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Excuse me for jumping in here.
CGM's lag about 15 to 20 mins behind actual blood glucose levels. So if your levels are going up and/or down it is unlikely to match a finger prick result closely.
If you spot that your CGM is showing your glucose level has been flat for while, try doing a finger prick test and see if it's a closer match.
CGM's do not measure actual blood glucose. They are looking at glucose in the interstitial fluids between skin cells so a tight conformance to real blood glucose levels may not always be possible.