CGM and finger stick different

[Sene]

. My readings from the Freestyle Libre2 CGM and manual readings are between 30-40 points different. Do I just accept the readings from the CGM and ignore my finger stick numbers? Will the readings get more in line after some time? Any help you can give me is most appreciated. Just started on my CGM this morning. My first time having one.

 

[Melgar]

Hi and welcome to the forum @Sene. We have a great community here, with a lot of knowledgeable members who are more than happy to answer any questions you may have.
If you don’t mind me asking, what are your blood sugar readings?

As for the different readings , there are a number of reasons this could be happening. Firstly, the CGM device has some accuracy issues for the first 24 hours, whilst the sensor filament ‘beds in’.Many members will attach a sensor 24 hours before the last sensor has finished. This is to allow the filament to settle. The sensor does settle down.

Secondly, your glucose meter analyze your blood sugar directly from your blood, whereas the CGM analyzes the blood sugar in your in interstitial fluid, which is the fluid around your cells. There is a time lag with the CGM, so it’s always going to be behind your finger prick readings. So that could account for the difference, especially if your blood sugars are rising or falling .

And thirdly, your blood sugar measuring devices have a 15% +/- allowable error against a lab device. Given the 15%-/+ allowable error , this can also account for the discrepancies.

Out of the two devices, I would always take the finger prick over my CGM devise.
Mel

 

[searley]

Sadly there will often be a difference.. one is measuring blood one is not! With you bg meter you can get different readings if you test different hands.. even bg meters have a margin of error

Cgm is good for a general overview and seeing trends, but if you feel different to the results you are seeing you should always do a proper bg test before making any treatment decisions

The higher your bg, the bigger the gap may be between the 2 readings

 

[Tony337]

Good morning and welcome @Sene
As others have said the finger prick test is more accurate but as i've been injecting myself with insulin for fifty years allow me to give you my view on the freestyle libre2 we both use.......

I adore it and because of it i have improved my overall readings and my last hba1c (average blood sugar over the last 3 months) was 39 or 5.7.
As has already been said pop a new sensor on 24 hours before activation then finger prick test and compare the results to the libre.
I only activate mine when i'm stable so for example if my level is 5.5 and i haven't got masses of fast acting insulin on board and i haven't just expended a load of energy and eaten a takeaway! i would then activate it.
Successful diabetes control is an equation of insulin exercise and food in my humble opinion and if you have too much of any of those when activating a libre then accuracy becomes questionable.

Nobody teaches you that but i'm starting from a good level, say the 5s, but if you are in the 12s and your finger prick test and libre are a long way away then you need professional advice.

I would like to know what you mean by 30-40 points?
lol i'm old school my level this second is 4.3 mmol/l and its no wonder people get confused as there are different ways of measuring your levels depending on which country you live in.

I saw a physio last year and when she discovered on her computer my hba1c level of 40 she told me i could do better!!
I was just glad she was a physio and not a diabetic specialist......lol

Alot to take in?
Perhaps but when you get to grips with analysing your own data and your readings improve it will become like breathing.

I wish you well

Tony

 

[Deleted member 527103]

I would like to know what you mean by 30-40 points?

The OP is not in the UK so is using mg/dl rather than the mmol/l we are familiar with.
I think the conversion is division by 18.
So, a variation of 30 to 40 mg/dl is equivalent to variation of 1.7 to 2.2 mmol/l.

But as said above, whether this is within the standard accuracy tolerance depends what the "true" BG is.
For example, if the "true" BG is 6.0, it could be reported by either meter anywhere between 5.1 an 6.9 whereas a "true" BG of 12 could be reported as anything between 10.2 and 13.8.
Remember, the finger prick meter we have been relying on for years, could always be reading high or low by up to 15%.

 

[Tony337]

The OP is not in the UK so is using mg/dl rather than the mmol/l we are familiar with.
I think the conversion is division by 18.
So, a variation of 30 to 40 mg/dl is equivalent to variation of 1.7 to 2.2 mmol/l.

@In Response Thanks
I really would not like to be learning about diabetes from scratch today and i mean that in the nicest possible way!

Tony

 

[becca59]

Two meters and Libre all taken at same time a few moments ago. Within 5 mins the Libre was matching the first monitor.