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Which to trust? Finger prick reading vs CGM

V

VrindaRaj

Newbie
Messages
1
Type of diabetes
Prediabetes
Treatment type
Diet only
Hello!

I’ve neglected and been in denial of pre diabetes that was diagnosed 5 years ago.

Something clicked recently and I found motivation to face reality and take control of my health.

Im eating better and exercising (from being a couch potato with a processed food addiction) but it’s only been a few weeks.

I’m using a LIBRE Pro CGM and Accu-Vue Instant monitor.

My finger prick readings are 15 to 30 mg/dl higher than my cgm readings even accounting that interstitial readings will lag blood by 20 minutes.

Which reading should I trust?

My objective is to not allow my blood sugar to breach 140 and achieve low glucose variability through lifestyle modifications. My blood glucose peaks about an hour after I eat. It’s confusing to see two different readings. According to my CGM I am achieving my goal everyday that I adhere to healthy eating. According to my Finger prick sensor I am not.

Exercise sends my blood sugar up to 180-220 as per my CGM and I don’t bother checking on the finger prick because I’ve read this is typical in pre diabetes and worth the trade-off.

Thank you for reading.
 
A few points to remember about CGMs like Libre
- whilst interstitial fluid is behind blood, what is reported is NOT behind. The algorithm used to make the conversion takes the delay into consideration by extrapolating the current trend
- our bodies can take a day or two to get used to the foreign object on our arm and Libre can be inaccurate during this time. This is why 8t is common to apply a sensor a day or two before activating it.
- CGMs are designed to be most accurate at "normal" levels. Anything outside 4 to 10 mmol/l (I think this 8s about 70 to 180 in the units you have quoted), can be over estimated and should be checked with a finger prick.
- Libre are factory calibrated. Our bodies are all different and some of us find "factory man" is not the same as us. Other CGMs allow calibration. There are 3rd party unofficial apps for Libre such as Shuggah that allow calibration.
- finger pricks are more accurate than Libre. Even Abbott says to check your Libre readings with finger pricks if Libre readings appear unexpected.
- everyone's BG varies, regardless of diabetes. Someone without diabetes can spike over 10 mmol/l occasionally if they eat a carby meal. Staying under 140bl ALL the time may not be realistic - you are trying to achieve better than a healthy pancreas.
 
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