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Type 1 Libre 2 sensor

Carl W

Carl W

Well-Known Member
Messages
122
Just a quick question, what do I do if my sensor keeps reading lower than what it is? First time using it was yesterday, and today it’s been reading lower than what it is. Do I take it off and apply the other one, thing is I’ve only been given two and told they have to last the month before getting more.
TIA
 
They frequently misbehave in the first 24 hours whilst your body settles down to the minor intrusion.

If the accuracy doesn't improve then record blood level, wait 10 minutes and take a scan. Do at least three of these then ring Abbott. Normally they will send you another if the discrepancy is outside their range.
 
You can report sensors to Abbott that are out by a large amount. However, there are (as frequently mentioned in threads about Libre and other CGMs) limitations which you need to be aware of.
Off the top of my head these include
- many of us find sensors can take a day or two to “bed in”. This is where our body gets used to having an alien object in our arm which can affect readings. For this reason, it is not uncommon to apply the sensor a day or two before activating it. As you only applied your sensor yesterday, this could be affecting your numbers.
- CGMs, including Libre, are calibrated to be most accurate between about 4 and 9mmol/l. Any reading outside this range could be inaccurate and should always be checked with a finger prick. If your numbers are higher than 9mmol/l, this could explain the issues you are seeing.
- CGMs use interstitial fluid to get readings. This is about 10 to 15 minutes behind finger pricks. Libre attempts to accommodate this delay by extrapolating the current graph and predicting the current reading. This works well if levels are stable but if your levels change direction, such as when you correct a hypo, the Libre readings can appear to take longer to recover.
- if you apply pressure to a sensor, it can give a false low reading. This is called a “compression low” and can occur at night when you lie on your arm.
- some Libre sensors are faulty. If you report this to Abbott, usually, they will replace them. i always consider the known limitations before reporting.
 
In Response said:
You can report sensors to Abbott that are out by a large amount. However, there are (as frequently mentioned in threads about Libre and other CGMs) limitations which you need to be aware of.
Off the top of my head these include
- many of us find sensors can take a day or two to “bed in”. This is where our body gets used to having an alien object in our arm which can affect readings. For this reason, it is not uncommon to apply the sensor a day or two before activating it. As you only applied your sensor yesterday, this could be affecting your numbers.
- CGMs, including Libre, are calibrated to be most accurate between about 4 and 9mmol/l. Any reading outside this range could be inaccurate and should always be checked with a finger prick. If your numbers are higher than 9mmol/l, this could explain the issues you are seeing.
- CGMs use interstitial fluid to get readings. This is about 10 to 15 minutes behind finger pricks. Libre attempts to accommodate this delay by extrapolating the current graph and predicting the current reading. This works well if levels are stable but if your levels change direction, such as when you correct a hypo, the Libre readings can appear to take longer to recover.
- if you apply pressure to a sensor, it can give a false low reading. This is called a “compression low” and can occur at night when you lie on your arm.
- some Libre sensors are faulty. If you report this to Abbott, usually, they will replace them. i always consider the known limitations before reporting.
Click to expand...

Thank you, it was reading 3.2, 3.4 and 3.5 when the finger pricks were reading 5.5, 5.7 and 5.8. So may wait another day before contacting Abbott.
 
barrym said:
They frequently misbehave in the first 24 hours whilst your body settles down to the minor intrusion.

If the accuracy doesn't improve then record blood level, wait 10 minutes and take a scan. Do at least three of these then ring Abbott. Normally they will send you another if the discrepancy is outside their range.
Click to expand...

Thanks, yeah I did 3 readings, while the sensor was reading in the 3’s the finger pricking was in the 5’s.
May leave it another day as it’s only been about 24 hours now since I first put it in. But the readings were very close yesterday compared to todays
 
As already stated, the sensor can give erratic reading for the first 24 hours or more, which is why I fit my next sensor around 6 hours before the current one expires, but others fit up to 24-48 in advance of their current sensor expires. Going forward I expect you will find what works best for you.

I have learnt that when a scan reading goes below 5, the sensor is erring on the side caution giving the user the time to act to head off a hypo. For that reason my low alarm is set to 5. That said, when the reading drops below 5 I always finger prick to confirm the sensor reading. Usually the sensor is reading lower than the finger prick and I personally think this is a safety feature inbuilt by Abbott.
 
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