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Blood Sugar changes-Freestyle Libre 2 vs Finger Prickle errors

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byeazucar

Member
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Hi everyone,

Hope you are all having a fantastic early Sunday.

To provide some context, my wife has been on a keto diet for several months now, we use to use finger prickle and then moved to Freestyle libre 2. In the beginning, we use both measurements, however after finding a significant accuracy between the both,m we decided to use only the sensor, as makes tracking much easier.

We were living abroad for few months and due to lifestyle and more daily exercise, sugar levels were pretty much below 5.5 mmol constantly throughout the day. We are now back in the UK and our daily exercise has unfortunately been reduced, bringing average sugar to around 6-6.3mmol

The sensor detected a spike in sugar (8.1mmol) last night when she took a Covonia Sugar Free cough drop around 1.5 hours after dinner. (Prior it was on 6s, with a non-carb dinner), the spike did not last more than 30 min, which makes me think the sucralose on the drops tricked her pancreas.

This morning to our surprise we got woken up by a high sugar alert of 8.2 mmol (this has never happened before, her sugar is always on the low 6 mmol. when waking up, and takes Glicazide to contr. l the morning spike) I decided to test blood on her finger and it was pretty similar 8.4 mmol.

Took Glicazide, and after 1h. sensor. still reports 8.4mmol and finger 8.0mmol (it is going down on the blood prickle and slightly. up on the sensor). Decided to make her a tea with unsweetened almond milk, as could help her pancreas to process food and stock tricking the body (if that was the case). Waiting 15 min and sensor read 6.0 mmol, which is more likely to her standards. (thinking maybe the pancreas reacted this morning to somehow the late night sugar-free cough drop and created a high spike in the morning??)

However the finger blood is reading now 10.2 mmol after the tea and 2h after Glicozide, and the Libre is reading 6 mmol.

I am very confused about the readings (libre seems more like the normal but the finger read is very high ) and makes me worried about all these weeks that we have been trusting only the reading. When I was seeing 6 mmol, could she be on her 10mmol or this might be a 1 off? What can be causing such a scenario? I will continue monitoring now both for the coming days and see if this was a 1 off, but at this time I am worried.

Her blood test is next week so we will find out more, but given she has advanced eye retinopathy, I get really worried each time I see anything above 7 mmol, even if it is a single time. Can such unusual scenarios make a big impact on her health/retinopathy issues?

Thank you in advance for your imputs
 
If this morning’s finger prick is higher than expected and higher than your wife feels and higher than the Libre, has she washed her hand and tried again? Finger prick meters can be wrong.

With regard to Libre accuracy, I find sensors vary and can drift so I always check their accuracy against finger pricks first thing each morning. I find no reason to double check all through the day. And they can be faulty.

I assume your wife is feeling unwell if she is taking a cough drop. This could explain her current higher than usual reading.

I would not stress about a spike over 7. People without diabetes can spike to 9 or 10. The stress of this extra checking and extra vigilance can cause her levels to rise.
 
Whilst the Libre can be accurate a lot of the time, it can be 'tricked', as you put it.

For instance, every time I walk up or downstairs in my house it registers this a Blood Sugar spike, literally every Sensor I've ever had. Similarly, I find my body temperature can affect readings on the Libre too.

Like In Response says, though. You should first of all check nothing's skewing your Blood Sugar Meter's readings.
 

Hi there,

Your wife could try washing hands & take a second test with the meter..?
I had something similar the other day after checking calibration with my L2 sensor forgetting to wash after a cleanup with recycling waste plastic..
 

Thank you, she has washed her hands now and both are on the same line, 6.4mmol on libre and 6.3mmol on the finger. Not sure if this was the case as we did multiple finger prickles and all were higher than the sensor (and above 8), however, there were some significant gaps between measures on the finger which makes me think maybe the wash hands was actually affecting? We tried different fingers though.

She has a mild cold, as well as being on her menstrual cycle, which could also be part of the problem. To add to it, her senson is new (installed yesterday, rather than 2 days prior end of the previous one as we usually do, as I am aware it can be slightly incorrect the first 2 days)

Moving forward we will conduct finger tests in the morning to be sure, I just got really worried as we have not seen a 10mmol (perhaps anything above 8.5 mmol in a couple of occasions) in the last 4 months

I look forward to getting her blood test results this coming week, currently Libre shows a A1C level of 5.1% with a 32 mg. If we are on that level on the test, I will be very happy
 
I always run higher when menstruating - a lot of people are more insulin resistant at this time. I don’t know if that was what your wife was experiencing, but if she had a cold at the same time I would guess combined they are the culprit?

I hope she feels better soon and sugars return to normal.
 

Thanks for your input, sometimes we have seen slightly higher levels of menstrual cycles, but nothing above high 6s I believe. Perhaps the addition to the cold on top is not helping. I have attached a chart for the last few weeks as a reference.

Thank you for the wishes, much appreciated
 

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I hope your wife’s blood test goes well @byeazucar .It does sound as if hand washing might be the issue - someone on this forum posted a couple of years back that a particular make and fragrance hand wash caused finger prick readings to be high - when he washed his hands with his usual soap it was normal.
Also, like others have mentioned, if she’s not feeling well that would cause higher readings. External Temperature too, a hot shower will cause a high Libre reading and a cold dip in the sea makes it plummet.
 
I can’t comment on the one aspect but when being Ill it’s common for blood sugar rises, so the cold could easily be impacting
 
Unfortunately both the fingerpricks and especially the FSL can be way of, even up to more than 40%.
The only way to get more accurate results is by using more meters.
First work out the bias of each one and then quadruplecheck your results.
 
Bubbleblower said:
Unfortunately both the fingerpricks and especially the FSL can be way of, even up to more than 40%.
The only way to get more accurate results is by using more meters.
First work out the bias of each one and then quadruplecheck your results.
Click to expand...
And become more anxious!
If I was concerned by meter’s accuracy I would rather use control solution to test and contact the manufacturer for a replacement if it was too far out.

byeazucar said:
I look forward to getting her blood test results this coming week, currently Libre shows a A1C level of 5.1% with a 32 mg. If we are on that level on the test, I will be very happy
Click to expand...
Hopefully, her numbers will be good but don’t be too disheartened if they are higher than Libre says.
Libre uses a different algorithm to approximate the HbA1C. Some find it close. My blood test was 10 higher than Libre guessed.
From then on, I ignored what Libre said about HbA1C and concentrated on time in range and being confident I was doing my best without letting diabetes take over my life.
 
In Response said:
And become more anxious!
Click to expand...

Are you talking from experience? I use 3 meters (fingerprick) to test the accuracy of my 4th meter (CGM) every 2 weeks, or when a reading makes no sense and then it takes away anxiety.

Control solution is not a very good solution because it also has a big margin of error,
the only way to get more accurate results is by using more meters, it's simply a matter of statistics.

For this reason they should also do several HbA1C tests (which aren't as accurate as you would expect either) to determine the HbA1C, it's ridiculous they don't, when they base their entire policy on this outcome.
 
I'm finding it very difficult to understand what you mean in your second sentence, and I'm not sure I'm entirely following how you're using the word meter. Could you elaborate, please?
 
Bubbleblower said:
Unfortunately both the fingerpricks and especially the FSL can be way of, even up to more than 40%.
The only way to get more accurate results is by using more meters.
First work out the bias of each one and then quadruplecheck your results.
Click to expand...
Where do you get your figured? Finger prick meters have an accuracy tolerance of 15%

https://www.diabetes.co.uk/blood-glucose-meters/blood-glucose-meter-accuracy.html

which could cause an impact but over time will likely balance out. Of course given their readings are snapshots and not continual they may well not be close to hba1c but for measuring impact of meals and for snapshot checks for those who need to know they do what they are supposed to

I don't know cgm tolerances but 40% sounds too high
 
Bubbleblower said:
Are you talking from experience?
Click to expand...
No. I have no need to be anxious about my diabetes. I trust my meter and, after nearly 20 years with Type 1, have no complications, am fitter than my friends and colleagues of a similar age who do not have diabetes, have a HbA1C lower than that considered to be the threshold for type 2 and don’t let my diabetes control my life.
 
Hi @Bubbleblower ,

You could try scanning or taking a reading on you sensor. Then 20 minutes later use one of your meters & do a blood test?
The results may possibly look a little closer in range..

Hope this helps.
 
Ah yes I suppose you used the following to come to that conclusion

Repeated measurements by one instrument. Assumptions 1-3 enable us to view each measurement as a sum
Zi=μ+Xi+Y
where i is an index denoting the measurement and ranges from 1 through n.

Notice that Y has no subscript because it is a property of the instrument itself: it doesn't change from one measurement to the other. We may compute the variance of the average of the measurements--conceived of as an average of these random variables Zi--as
Var(Z¯)=1nσ2+τ2.
As n gets larger, σ2/n grows smaller.

Moreover, if we take expectations in the sense of what an arbitrarily large number of measurements would produce on average,
E[Z¯]=μ+Y
shows that even the average is biased (unless you were lucky enough to draw an instrument with Y≈0--but you can't know that).

The moral of this calculation is that averaging measurements from one instrument reduces the imprecision but has no effect on the accuracy.

Independent measurements by multiple instruments. Now i indexes both the measurement and the instrument. Accordingly,
Zi=μ+Xi+Yi.
Now
Var(Z¯)=1nσ2+1nτ2
and (in the same sense as before, taking an arbitrarily large number of instruments),
E[Z¯]=μ.
As n gets larger, both σ2/n and τ2/n grow smaller. Regardless, the expected value of the measurement is correct: Z¯ is more likely to be accurate in this case.

Thus, averaging measurements from multiple instruments reduces the imprecision and improves the accuracy.

The decision seems clear: when you have the choice, use multiple instruments. Making repeated measurements from the same instrument is no substitute.

But I say why bother just gets you very sore fingers.
 
Andydragon said:
Where do you get your figured? Finger prick meters have an accuracy tolerance of 15%
Click to expand...
The 40% number comes from Abbott, who has (or had) a table on their site that showed 98% of all results were within 40%, iow 2% was more than 40% off.

<Edit> I can’t find it back so fast, but here you can also see some readings are more than 40% off:
</edit>

Oh, and in labs the result can be off as much as 20%, which is shocking.

JohnEGreen said:
But I say why bother just gets you very sore fingers.
Click to expand...

From one fingerprick every two weeks?
Of course the math is very simple;

Say you have two meters.
If they are for example within a ±10% range (98% of the time) and the readings are 6 and 7 the BG is between 6,3 and 6,6. While if you only use one meter and the reading is 7 it is between 6,3 and 7,7.

I rather know my BG within a 0,3 margin than a 1,4 margin.
 
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Then again if you have an infinit number of meters and take an infinite number of blood tests then the error though becoming infinately small is always going to be greater than zero being asymptotic to zero so as you can never eliminate error and you will never get a difinitivly accurate reading why strive for the unatainable just accept that there is always going to be errors and get on with it.

Of course the above scenario is of course plainly an impossibility as you would die from blood loss long before you could obtain the required amount of blood tests.and still would not know what your blood sugar level accually was.
 
JohnEGreen said:
The decision seems clear: when you have the choice, use multiple instruments. Making repeated measurements from the same instrument is no substitute.
Click to expand...
But it'll probably show you if you have a one off errant reading because of contaminants on your hands.
Some meters read a bit higher than others (my current reader definitely reads a bit higher than the freestyle lite I had before coming to NZ) but it definitely allows me to double check before I treat major lows or highs as diagnosed by my cgm.
 
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