Observations on Libre CGM, feedback needed

[nsh2111]

Hello All,

Returning after some time here. I have just started using a libre ( using the free one time sensor they send) for now. I have noticed few things and I am now confused and need some feedback. Please note I am T2, and without any medication. Low to moderate carbs.


1. Started the sensor from Friday morning and I noticed that my sensor readings are always 1.5/2 points higher than the finger prick. I read that it takes a day or two stabilise but still not sure if its generally higher?

2. I do regular exercise. Both aerobics ( spinning/tennis/body pump class etc) + weight training. My BG levels go higher during that time and then stay higher for an extended amount of time, Not sure what can be done. I do exercise to keep the BG level in check but it seems to be having opposite effect.

3. Friday evening spike was after a carb dinner. The spike above 10 mmol was on Saturday morning was after tennis and a weights in gym . The evening spike was after a fairy carb rich dinner.

4. Sunday morning spike was after a body pump class.

Thanks

 

[barrym]

I’m no expert in what a T2 or even an ‘non-diabetic’ would look like. Having said that, when talking to my consultant on many occasions over the years, she insists that spikes like that are perfectly normal. Maintaining high levels for long periods is the bad thing.

I dream of graphs like that.

 

[eventhorizon]

Hi!

The L2 is not perfect but it is very good! The discrepancies you noticed are well within the realms of acceptable.

The spikes are just that. Steep rise followed, immediately, by a steep fall back into target. It's the longer lingering highs for hours you don't want.

 

[jaywak]

As the two previous posts have said I don't think you have anything to worry about it just shows your body is working well and your liver is giving you a boost of glucose when you need it even getting out of bed in the morning will do that to a lot of us .

 

[In Response]

@nsh2111 welcome
You mention that, following use of the Libre, you are confused but have not explained what has confused you.
As others have said, there is nothing to worry about from your graphs.

However, have you considered the frequently mentioned limitations of all CGMs including Libre?
- insertion trauma - it is common for our body to react to the trauma of having an alien object inserted in our arm which can affect the readings for the first 24 to 48 hours after insertion. These may appear random. Some people have no issues with this but others find it useful to activate the sensor the day after applying it.
- compression lows - I have not spotted any of these in your graphs but still worth being aware of these - if pressure is applied to a sensor, it can block the flow of interstitial fluid which can result in false lows being recorded. This is most common at night when you lie on your arm as you turn over in our sleep. These are easily spotted on your graphs because they are a sudden drop followed by a sudden rise when you turn over again.
- ISR delay - CGMs do not read Blood Glucose (BG) they read Interstitial Fluid Readings (ISR), Changes in BG are reflected about 15 minutes afterwards in ISR. Libre accommodates this delay within the algorithm it uses to convert form ISR to BG by extrapolating the current trend. This works most of the time unless the trend direction changed in the last 15 minutes. This can result in a delay to detect change of direction and an over estimation of the high or low which is later corrected.
- normal readings - Libre is factory calibrated to be most accurate for "normal" readings which are between about 4 and 9 mmol/l. Outside of this, Libre have a tendency to over report highs and lows.
- factory calibration - whilst out bodies differ, it was decided to factory calibrate Libre and unlike other CGMs not allow calibration against finger pricks. However, some of us find that our bodies differ significantly from ""factory man" and find large discrepancies between what Libre reports and what finger pricks report.
- 15% accuracy - all meters must comply to a standard of 15% accuracy. Therefore, if you do compare Libre with a finger prick, you need to consider that one could be 15% high and the other could be 15% low which can show a significant absolute difference, especially at high levels.

The other thing I would mention is that you are checking BG whilst exercising. Please bear in mind that exercise has different affects on BG depending upon type, duration and fitness at that activity. Resistance exercise, short exercise, stop-start activities and anything which makes you uncomfortable are likely to make your BG rise whereas longer term steady cardio is likely to make your BG fall.

Finally, be aware that other things such as stress and illness can affect BG.

 

[sgm14]

I do exercise to keep the BG level in check but it seems to be having opposite effect.

If that is the only purpose of the exercise, then you could try less intense exercise. Things like lifting heavy weights and sprints can produce a lot of adrenaline which causes your blood glucose to increase.

I remember reading about a professional football who sometimes took insulin before a football game, but I'm not sure what a non-insulin user can do to counter this if you want to do this type of exercise for other reasons.

But looking at your graphs, it doesn't look like your blood sugar stays high after the workout, so it doesn't look like you need to do anything.

I don't think you should consider spikes as something terrible to be avoided at all costs. One misconception that I had when I was first diagnosed was that I thought non-diabetics never, ever had blood sugar levels below 4 or above 10 and was surprised to find that was not true.

 

[barrym]

On a slightly off topic point, you refer to exercise, and as also been mention, exercise can cause BG rises.

I think a differentiation between exercise and activity should be drawn. For example I call walking an activity. Many find walking, or easy cycling, maybe gentle swimming are beneficial to BG, whereas extreme exercise can have the opposite effect.

An amateur explanation is that activity improves absorption of whatever insulin you've got on board, but exercise puts demands on the body which may involve the body dumping glucose to help out!

There! Having said all that no one will ever listen to me again .

 

[In Response]

For example I call walking an activity. Many find walking, or easy cycling, maybe gentle swimming are beneficial to BG, whereas extreme exercise can have the opposite effect.

Let's be careful not to confuse the immediate affect of exercise on BG and the medium/longer term impact.
As you have identified (and I explained above) some exercise can cause BG to rise and some may cause it to fall. It is not necessarily about the ëxtremity pf the exercise but about the type, duration and your fitness.
However, the impact of exercise on BG is longer. It is common for exercise to lower BG (or in the case of someone with Type 1, their insulin requirements) for up to 48 hours AFTER exercise.
I participate in a few different activities - cycling will, normally, reduce my BG whereas climbing will increase it. However, I need to be aware of low BG overnight after either type of exercise.

 

[In Response]

There! Having said all that no one will ever listen to me again .

I listened

 

[barrym]

Let's be careful not to confuse the immediate affect of exercise on BG and the medium/longer term impact.
As you have identified (and I explained above) some exercise can cause BG to rise and some may cause it to fall. It is not necessarily about the ëxtremity pf the exercise but about the type, duration and your fitness.
However, the impact of exercise on BG is longer. It is common for exercise to lower BG (or in the case of someone with Type 1, their insulin requirements) for up to 48 hours AFTER exercise.
I participate in a few different activities - cycling will, normally, reduce my BG whereas climbing will increase it. However, I need to be aware of low BG overnight after either type of exercise.

My cycling is now 3 or 4 miles at a time a few times a week. Just to get into town, or other local travel. All in full normal clothes. No punishing 40 milers any more which as you say, are all together different.

 

[nsh2111]

Thanks for all the comments.

@barrym I exercise to keep myself fit but yes also I have read that exercise helps improve insulin sensitivity.

May be I should not worry too much about these spikes. Its just that libre makes it amber as it goes certain range.

@In Response you raise a good point about factory calibrated device.


It seems I just need to watch it for few days and also try different foods, while I have it to see what effect each has only body.

 

[Cumbrianjudith]

Can I slip in here with another Libre 2 query? Some lovely replies here that was information new to me ( even tho just been on 4 week diabetic course) as a new Libre 2 user on type 3c diabetes: I didn’t know it’s ISR and not BG they measure, nor the time delay or 15% +/- accuracy etc! I am now on my 4 th monitor and changed from humulin 1 to Toujeo and Fiasp insulins, and thought after 7 weeks fine tuning was almost getting the balance right with the vast majority of readings in the green 4-10 zone, taking 40 units as background and 6 ish with meals. I intermittent fast 5 days a week with swimming and no food for 16 hours. Then last night, 4th after adjusting Toujeo a bit upwards from 37 (when got no hypos but some hypers) I was woken by alarm reading 2s ( ate some nearby shortbread) , went back to sleep and off it went again within the hour ( more sugar rich snack), and again a bit later when had to get up properly and had bread with honey( huge spike). Then off to swim with BG in 10s, and for first time since wearing monitor doing exactly same swim of 45 mins BG was 2.9 getting out of pool ( 3 big glucose sweets designed for hypos). Has gone off again at 3.8 only 1 hour after eating cottage pie dinner…. I thought this all very odd and did a conventional BG finger tip blood test which recorded 6.8. The question is have I got a rogue monitor that is misbehaving, or has my body suddenly ‘changed’ in response to insulin? I am definitely not keen on stuffing myself with sweet foodstuffs. This am reduced the Toujeo down to 38. Any suggestions, I am on my own now to adjust meds.?

 

[Antje77]

I thought this all very odd and did a conventional BG finger tip blood test which recorded 6.8. The question is have I got a rogue monitor that is misbehaving, or has my body suddenly ‘changed’ in response to insulin?

There is no way to tell with only one fingerprick test to compare your sensor with.
I'd do some more testing to see if your sensor is off or if it's your BG.
Good luck!

 

[HairySmurf]

Let's be careful not to confuse the immediate affect of exercise on BG and the medium/longer term impact.
As you have identified (and I explained above) some exercise can cause BG to rise and some may cause it to fall. It is not necessarily about the ëxtremity pf the exercise but about the type, duration and your fitness.
However, the impact of exercise on BG is longer. It is common for exercise to lower BG (or in the case of someone with Type 1, their insulin requirements) for up to 48 hours AFTER exercise.
I participate in a few different activities - cycling will, normally, reduce my BG whereas climbing will increase it. However, I need to be aware of low BG overnight after either type of exercise.

Indeed - it's the longer term impacts that make exercise of any type worthwhile. Exercise reduces insulin resistance and depletes glycogen stores in muscle tissue, which helps to lower BG levels for a considerable period of time afterwards as the muscle tissue efficiently sponges up glucose to replenish glycogen stores.

In Dr. David Cavan's book he states that for a Type 2, aerobic exercise will drop HbA1c by 8 mmol/mol, resistance training will drop it by 6 mmol/mol, and the two type combined will drop it by 9 mmol/mol. He states that a minimum of 150 minutes of exercise per week is needed to see that level of improvement. He doesn't give a reference for these numbers so I can't check which research he got those numbers from.