My continuous blood glucose monitor

[lordburnside]

Hi,

I just thought I had better try one of these gadgets. Using the old stick method gave me high readings between 7 and 12! My GCM says I am 5 or less most of the time and I have just dropped to 3.8 and a gentle alarm went off. I need to eat but its nearly lunchtime.
My breakfast of yoghurt, rasps and oats raised my reading from 5 to 8.5 and went back within 2 hours. Coffee and 3 aniseed balls (to take away the coffee taste!) made the tiniest blip of 0.4. I am checking out my lunch which is a salad with chicken to see if that breaks the upper limit. If I keep within readings of say 4 and 9 that is great? If I can do that for 3 months to my next blood test will my doctor say I am no longer diabetic or is there more to it than that?

I take no medication yet. My weight is down 10lbs but plateauing. I am walking 4 miles a day.
I am obviously not eating like I used to but I can live with this (maybe!) but miss the wine/beer/potatoes/dinners!

 

[Bruce Stephens]

Using the old stick method gave me high readings between 7 and 12! My GCM says I am 5 or less most of the time and I have just dropped to 3.8 and a gentle alarm went off.

Compare with test strips now and again. It may just be the CGM sensor isn't reading very accurately (in which case you should report it to the manufacturer, and they'll want to have comparisons with test strip readings).

 

[helli]

@lordburnside have you recently applied your sensor?
If so, you may be experiencing "insertion trauma" which can affect your readings.
It is not uncommon for our bodies to react to the alien object we just inserted in our arms which can affect teh reported readings. This is why some of us apply our sensors a day or two before activation: to give our bodies a chance to get used to the alien object so our readings are more reliable.

You may find this thread about limitations with CGMs useful. Sadly, physics does not allow absolute accuracy all the time so it is important to understand the limitations of CGMs.

 

[John Gray]

All the Libre 2 sensors I've used over the last year give figures lower than the finger-prick method, often as much as 2 mmol/L lower.
One just has to allow for this - like observing that even when the Libre 2 sensor says 3.1 I'm probably not having a hypo! [Since you are not on meds, this is irrelevant...!}

 

[helli]

I have noticed there are two types of people using LIbre - those who find it is always lower than finger pricks and those who find it is always higher than finger pricks.
Given all glucose meters comply with a standard to be +/-15% accurate, I wonder whether the difference is how Libre sensors react to different people or whether it is the finger prick meters reading at positive or negative end or accuracy.

The other thing to remember with this is that the accuracy is a percentage, rather than an absolute number. If the "true" reading is 10mmol/l and acceptable reading on any meter could be anywhere between 8.5 and 11.5 (more than a difference of 2 mmol/l). This does not mean there is a problem with either meter.

 

[lordburnside]

Compare with test strips now and again. It may just be the CGM sensor isn't reading very accurately (in which case you should report it to the manufacturer, and they'll want to have comparisons with test strip readings).

Thanks for the reply. I tend to think the CGM is correct as I felt off as the warning sounded at 3.8. After lunch I feel ok. My monitor is back down to 4.4 at the moment. Its an indication of what foods are good or bad. My lunch was salad and the machine went up to 5.2 but my breakfast sent it to 8.9 so no oats for me tomorrow!

 

[helli]

Thanks for the reply. I tend to think the CGM is correct as I felt off as the warning sounded at 3.8. After lunch I feel ok. My monitor is back down to 4.4 at the moment. Its an indication of what foods are good or bad. My lunch was salad and the machine went up to 5.2 but my breakfast sent it to 8.9 so no oats for me tomorrow!

But if you are used to running between 7 and 12, you could have been 5.5 and experiencing a false hypo.
Even though you are not managing our diabetes with medication, I recommend checking your CGM against finger pricks before getting lulled into a false security that your body is managing better than it is.

 

[lordburnside]

But if you are used to running between 7 and 12, you could have been 5.5 and experiencing a false hypo.
Even though you are not managing our diabetes with medication, I recommend checking your CGM against finger pricks before getting lulled into a false security that your body is managing better than it is.

Thanks I will do that.

 

[Leadinglights]

Thanks for the reply. I tend to think the CGM is correct as I felt off as the warning sounded at 3.8. After lunch I feel ok. My monitor is back down to 4.4 at the moment. Its an indication of what foods are good or bad. My lunch was salad and the machine went up to 5.2 but my breakfast sent it to 8.9 so no oats for me tomorrow!

You may be looking at levels which are more stringent than needed. My comment about the oats assumed the level over 8.5 was after 2 hours but you now say it was back down after 2 hours.
You are aiming at 4-7 before meals and morning/fasting and no more than 8-8.5 2 hours post meal. If levels are higher than that the guidance is no more than 2-3mmol/l from before eating to 2 hours after eating.

 

[Proud to be erratic]

I have noticed there are two types of people using LIbre - those who find it is always lower than finger pricks and those who find it is always higher than finger pricks.
Given all glucose meters comply with a standard to be +/-15% accurate, I wonder whether the difference is how Libre sensors react to different people or whether it is the finger prick meters reading at positive or negative end or accuracy.

If only for completeness I was a 3rd type, @helli, when I had Libre 2. I might start and stay high or start and stay low; with either my readings might be within 2mmol/L or could be 4 or 5 units adrift, at which latter point I would routinely ask for a replacement. I could also start high and become low within the 14 days - or vice versa; in these circumstances I felt a sensor was simply not fit for purpose because I would never be sure even roughly where I stood without FPs frequently.

I accept now that it was my body and Libre not being compatible, although early on I thought it was poor quality control from Abbott

I'm now provided with Dexcom G7 which proves to me that there is a reliable CGM package that I can trust. My one issue with G7 has been in the last 6 months the phone app has failed and frozen itself, 5 times demanding a factory reset. With a wipe of all my current data on the app - Grrrr. The most recent was yesterday. I believe this is nothing to do with the sensors compatibility with me; but an app and android argument!
The factory reset needs me to have the password to access Dexcom to hand (and the app prevents my phone from memorising that for so-called security reasons), needs the unique pin no for pairing with the sensor and the start-up sequence is laborious and time consuming. It treats me as a complete newcomer and requires me to watch various videos, acknowledge each tiny basic instruction and waste 22+ minutes of my life answering 'Accept' or 'Continue'; then it provides me many "tips and hints" that I simply don't need butvwhih prevent me looking at the displayed reading until the tip is acknowledged. All in all this aspect of G7, starting wirh the factory results being imposed, is pretty infuriating.

 

[SimonP]

I am also like @Proud to be erratic not always low or high, though I always have to eventually change the sensor if it's reading low as XDrip+ can only do so much calibration before it gives up (the limit being that when the sensor reads off-scale low, it can't need to be calibrated up so much that it will no longer warn you when you are actually low.) so this is probably what I tend to mention and comment on.

My current sensor is reading a bit high at the moment, but I must say I've found the sensors over the last 3 months+ to be pretty good (and also since now overlaying the 1min data on top of the 5min data I can see that some of the calibrations I might have done in the past would not have been at the right time).

They sometimes seem to gain an offset after a particularly rapid change in blood glucose (which then results in the sensor going offline for a bit), but usually manage to get rid of the offset if there's another rapid change, so I generally try to not bother calibrating these days unless it's a prolonged trend one way or the other.

 

[Kol]

Thanks for the reply. I tend to think the CGM is correct as I felt off as the warning sounded at 3.8. After lunch I feel ok. My monitor is back down to 4.4 at the moment. Its an indication of what foods are good or bad. My lunch was salad and the machine went up to 5.2 but my breakfast sent it to 8.9 so no oats for me tomorrow!

Hi,

To be honest I would be more likely to think a finger prick with a meter to be more accurate, as all situations where a unexpected CGM reading is displayed the advice is to double check against blood.

Also as @Bruce Stephens said Abbott will require blood glucose meter readings as comparison when reporting a sensor fault.

 

[PerSpinasAdAstra]

I have noticed there are two types of people using LIbre - those who find it is always lower than finger pricks and those who find it is always higher than finger pricks.
Given all glucose meters comply with a standard to be +/-15% accurate, I wonder whether the difference is how Libre sensors react to different people or whether it is the finger prick meters reading at positive or negative end or accuracy.

The other thing to remember with this is that the accuracy is a percentage, rather than an absolute number. If the "true" reading is 10mmol/l and acceptable reading on any meter could be anywhere between 8.5 and 11.5 (more than a difference of 2 mmol/l). This does not mean there is a problem with either meter.

I've only had one Libre 2 but found that it gave me numbers that were consistently lower than my finger prick reader by around 0.5 mmol/L on average, particularly my fasting numbers. I was curious to learn which device was more accurate so I did some reading to try to identify the most accurate finger prick reader available and order one to compare with the one I have. I learned that the +/-15% figure is the bare minimum necessary for ISO compliance, that some meters are much more accurate than this figure, and that different meters seem to be more or less accurate depending on the glucose concentration being measured - i.e. some meters are more accurate at lower concentrations and some at higher.

I settled on the Contour Next as (according to the best information I could find) the most generally-accurate meter available for which test strips are reimbursed by the HSE (Irish equivalent of the NHS). The manufacturer claims an accuracy of between 5% and 8%, plus or minus. I ordered one and a pot of strips and for the past week I've tested each drop of blood twice - once with the Contour Next and once with my existing meter, a Glucomen Areo GK. I found that the Next gave me readings that were around 0.5 mmol/L lower on average, than the Glucomen. It would seem for me at least that the one Libre sensor I tried gave me numbers that match the Contour Next, but not my existing meter, with the difference being most apparent when testing my fasting BG levels.

This leads me to wonder if the phenomenon of people finding the Libre is always higher or always lower than finger prick readings just have meters that tend to read higher or lower than the Libre at their average BG level.

 

[Docb]

@PerSpinasAdAstra - technically you are not looking at accuracy. You can only do that if you test against a standard where you have measured the thing you are looking for by some absolute method. What you are doing is comparing measurements from a system which is continually changing and for which you do not have an accurate value ofBG.

I suspect that if you did a statistically designed experiment you might find that the differences you are seeing are perhaps not as significant as they appear to be at first sight.

Much, much more important is the question of whatever the numbers you get from any system, can you use them to make sensible decisions. The answer to that must be a resounding yes - except for the wrist watches which claim to monitor blood glucose.

To me the real benefit of continuous monitors is that they give a far better indication of how things are changing and for anybody on insulin therapy that must be more important than its best guess at what the blood glucose level might be.

 

[lordburnside]

@PerSpinasAdAstra - technically you are not looking at accuracy. You can only do that if you test against a standard where you have measured the thing you are looking for by some absolute method. What you are doing is comparing measurements from a system which is continually changing and for which you do not have an accurate value ofBG.

I suspect that if you did a statistically designed experiment you might find that the differences you are seeing are perhaps not as significant as they appear to be at first sight.

Much, much more important is the question of whatever the numbers you get from any system, can you use them to make sensible decisions. The answer to that must be a resounding yes - except for the wrist watches which claim to monitor blood glucose.

To me the real benefit of continuous monitors is that they give a far better indication of how things are changing and for anybody on insulin therapy that must be more important than its best guess at what the blood glucose level might be.

I was just trying the CGM out. They are far too expensive to run all the time. I just wanted to see how my BG moved and came back down again and to try and lower the peaks. My current device has 15 days to go and I am on holiday in London this evening. I will be drinking beer regularly but will be careful with food most of the time! Obviously I will walk 100 miles while I am there which should help. On my return I will be a very good boy until my HBA1C blood test at the end of April. It should give a better reading but my blood will still have some old more sugary blood in it! so it wont necessarily be under 48 (It was 55 after Christmas).
I like being thinner and walking is a new thing! I don't miss the potatoes etc yet! The warmer weather is coming so I can walk more, garden more. I think I am eating better and my portion sizes are nearly correct. Before they were 50% too big and accompanied by wineand followed by crisps and cheese and biscuits! I am surprised I was only 16 stone. Heading (rather slowly) towards 14stone now.
I can't start my modelling career just yet!

 

[SimonP]

I suspect that if you did a statistically designed experiment you might find that the differences you are seeing are perhaps not as significant as they appear to be at first sight.

Before enabling the 1min data in XDrip+ (via Juggluco) I would habitually calibrate as there was often an offset (even with the data aligned in XDrip+ and looking at flat regions). Now that I can see how much by BG wobbles around in the "flat" regions I don't usually need to calibrate sensors.

I will calibrate those that are way off (like >| 2 mmol/l |) and may be above or below the actual value, though they do tend to converge back to the actual value eventually (often after some fast transients force them offline and they presumably do some sort of calibration reset internally.)

There are still occasionally those that have a large offset that just gets bigger until I can no longer calibrate them, though this generally only requires a new sensor if they read too low as otherwise they can be corrected for (and still allow hypo detection). There is therefore probably some reporting bias in what I say as my replacements are for sensors that read low.

I do have all the data from my entire usage, I must sit down and generate some statistics for my n=1 (patients) sample.

 

[everydayupsanddowns]

My current device has 15 days to go and I am on holiday in London this evening. I will be drinking beer regularly but will be careful with food most of the time! Obviously I will walk 100 miles while I am there which should help. On my return I will be a very good boy until my HBA1C blood test at the end of April.

Hope you get some useful information from your sensor experiment @lordburnside 🙂