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Can a fingerprick meter be faulty? Don't know which to believe!

V

Vectian

Well-Known Member
Messages
92
Type of diabetes
LADA
Treatment type
Diet only
I know that CGM readings are not so accurate, so I wanted to double check it was roughly in the right area. CGM said 4.9 on waking, then up to 5.7 after I had got up. First fingerprick reading was 7.5, thought that seems high, so waited 15 mins for CGM to catch up and it said 5.8. Then I tested again with 2 different meters, quickly one after another so 5 seconds inbetween, one said 6.5 and the first one (black) now 8.1. How am I supposed to know which is right, or if any are giving me faulty readings? Has anyone had a fingerprick meter give readings which are far out? I know there is a certain tolerance but there is a difference of 2.3 there (the CGM said 5.8 15 mins later).

Fasting 5.8 is good, 8.1 isn't and needs sorting but if you can't rely on the numbers what are you supposed to do?
 

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Meters should generally always be considered more accurate than the CGM's - the meters showed 6.5 and 8.1 which are not too far off each - for blood glucose meters to be considered accurate they should be within 15% of the actual value - well 6.5 and 8.1 are within 15% of about 7.3 (the mid value of those two readings), so I'd guess your value was actually somewhere between the two blood glucose meter readings
 
Rokaab said:
Meters should generally always be considered more accurate than the CGM's - the meters showed 6.5 and 8.1 which are not too far off each - for blood glucose meters to be considered accurate they should be within 15% of the actual value - well 6.5 and 8.1 are within 15% of about 7.3 (the mid value of those two readings), so I'd guess your value was actually somewhere between the two blood glucose meter readings
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That would mean that several CGM sensors in a row were all consistently reading 1.5 - 2 too low. I know they are not accurate for snapshot readings but over the course of months? In the past I have measured CGM against fingerprick and it's been fairly close, at different times of the day. It's so difficult to make any treatment judgements based on such conflicting numbers, if I assume the morning reading was 7.3 and adjust to get it to 5 something the CGM would say I'm in hypo all night long, it is already often in the 4s overnight.
 
My libres often read 2mmol/l lower and up to 4mmol/l lower (at which point I have them replaced - I have had sensors with ever larger offsets) than actual BG values (looking at stable periods to remove uncertainties around delay times). This is an unfortunate fact of life with CGMs, I'm surprised people aren't advised to calibrate them form time to time using blood tests.
 
You need to make sure to wash and dry your fingers before doing a test - sweat and food residues can add a couple of units.
On the other hand if your BG is low - that's real and possibly even lower if hands are not washed. (I sound like the matron at my old school)
 
Libres (and all CGM) have caveats - not accurate at the start (insertion trauma so not as accurate), then more accurate in the middle of the 14 days, then less accurate again as you heal around them.

I also find they need calibrating (so they say the correct readings during changes over the 14 days) so use xDrip to use and interpret the readings.

Also remember they are 'behind' a blood test (I estimate mine to read 20 mins in the past) as reading interstitial fluid rather than blood.

Then as @Jasmin2000 says - other stuff can get in the way - for a baseline test try washing and drying hands and use 2 different fingers (one for each BG machine) and see what happens - they will almost always be slightly different no matter what you do, but shouldn't be 'that' different.

Looking at your photo, Libre and SafeAQ look about right - the smartduo is questionable.
 
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