CGM sensors - are they accurate?

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10
I’m Confused!! My daughter just been to her quarterly diabetic check-up. We expected a Hba1C around 52 from her sensor data, but the quick test said 61, and both us, doctor, and nurse thought it was wrong, so got a lab test, which came back as 62! She has only been wearing her sensor about 5 and a half day per week, so there could be some discrepancy with that, but not that much.
Anyone else had this problem / any suggestions to why??
She is on a Medtronic 640G pump and her sensors are Guardian3.
 

Rokaab

Well-Known Member
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2,159
Type of diabetes
Type 1
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They are accurate to a certain extent, for some they are for more accurate than they are for others, I think I've read for some people they just don't work very well. Mine (I use the libre) normally shows 0.5-1 lower than I am, but its consistent so I know how to deal with it. Are you verifying some of the results with blood tests?

And yes if she's only wearing then 5.5 days out of 7 that could make a difference as you only have 78% of the actual data, she could be higher on the other day and a half which could make a difference - whether it'd be that much difference though I couldn't say.
 
M

Member496333

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Worth keeping in mind that HbA1c is actually an indirect measurement and is not always fully representative of average blood glucose. There are always potential errors and tolerances in any test measurements.
 

Antje77

Oracle
Retired Moderator
Messages
19,284
Type of diabetes
LADA
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Insulin
Hi, I use the Libre and see the same. My estimated hba1c's from Libre have been 8 mmol/mol lower than the tested ones from hospital.

I do fingerpricks quite often alongside the Libre and the difference in estimated and measured hba1c is what I would expect from the difference between Libre and fingerpricks.

It seems for some of us CGM's read consistently lower than blood, for some of us they read higher and for some they are spot on.
 
M

Member496333

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It seems for some of us CGM's read consistently lower than blood, for some of us they read higher and for some they are spot on.

I have often wondered if CGMs might generally tend to be weighted more toward reading lower than higher in order to be on the safer side of alerting the user to hypoglycaemia. Just an idle thought...
 

Jollymon

Well-Known Member
Messages
431
Type of diabetes
Type 1
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Pump
Dislikes
Not having good chocolate, and not cycling
Cgm works on interstitial fluid, which isn’t blood sugar. Don’t confuse the 2.

For some cgm works great, and for others it’s not so good. Based on the discrepancy in the readings and how you were using it to attempt to predict a1c, maybe you’re not in the “it works great” group. At least try to learn as much as you can from it before giving up on it.
 

geekypants

Member
Messages
11
Type of diabetes
Type 1
Treatment type
Pump
I fall into the category of people whom CGM isn't that accurate for, with similar discrepancies in A1C stuff.

I still find it really useful for trends though. I was without one for a week there and it made me realise how reliant I am on it for confidence with corrections.
 
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