Erratic CGM Readings

[p4ul]

Following some advice on this forum, I bought a Dexcom G7 to see how my body reacts to my normal diet, so I have some data to make changes that I know are needed.

Apparently, I didn't like one of my staples; honey chicken with boiled rice last night - you can see the spike on the image. I also discovered that my breakfasts needed some attention; they were far too carby and over a short period of time. So this morning, I had:
2 ryvita with a light laughing cow triangle
150g vanilla greek yoghurt
2 boiled eggs with mustard/light mayo
Ufit premixed protein shake
Cup of decaf coffee
I ate this over the course of about 45 minutes.

The zoomed in image shows an erratic BG (although all within range), and my question is whether this is normal as my trace for the past few days has been quite steady. I don't particularly feel anything symptomatic to be concerned about but thought I would ask you lovely people to take a glance.

 

[Leadinglights]

With the details you get from the CGMs it is easy to mislead yourself in what you are seeing that is just the normal process of digestion of different foods which will be at varying speeds being a combination of fast releasing glucose as in the carbs in the protein shake which is almost all sugar with the proteins in that and the eggs.
As Type 2 unless you are taking insulin then the post meal 2 hour reading is what people take account of as being no more than 2-3mmol/l more than before eating or no more than 8-8.5mmol/l. It is hard to see from your pictures if that is the case.

 

[p4ul]

With the details you get from the CGMs it is easy to mislead yourself in what you are seeing that is just the normal process of digestion of different foods which will be at varying speeds being a combination of fast releasing glucose as in the carbs in the protein shake which is almost all sugar with the proteins in that and the eggs.
As Type 2 unless you are taking insulin then the post meal 2 hour reading is what people take account of as being no more than 2-3mmol/l more than before eating or no more than 8-8.5mmol/l. It is hard to see from your pictures if that is the case.

Ah. The glucose absorption rates makes perfect sense! Thanks for that.

I ate breakfast 7:30 - 8:00. At 7:30, I was on 5.9; at 10am, I was 7.3. All good by those criteria!

 

[Lucyr]

Apparently, I didn't like one of my staples; honey chicken with boiled rice last night - you can see the spike on the image.

The image doesn’t really tell us anything because the spike came back down. It’s what your blood sugar is at the 2hr mark that is used.

 

[PerSpinasAdAstra]

I tend to see erratic readings like that when a lot of things are happening at once. Example - rushing to get to a morning doctors appointment: eat breakfast which causes a rise to begin after 20 to 30 minutes, have a hot shower which messes with the sensor readings temporarily due to rapid temperature changes, rush about trying to get ready to get out the door which might cause a change due to hormones (adrenaline and/or cortisol - 'fight or flight' and/or 'stress' hormones), walk to the doctor's office which will push levels down quickly following a meal due to the moderate exercise, then sit down in the waiting room which might cause another rise after the exercise if I'm still digesting my breakfast and carbs are still entering the bloodstream. The number of factors which can influence your blood glucose levels is very long.

Worth noting also though that sometimes the sensor just produces erratic readings, particularly in the first 24 hours and due to issues like 'compression lows' - pressure on the site where the sensor is placed will reduce circulation in the fatty tissue under the skin and cause low readings, which spring back up quickly when the pressure stops.

If you're not on insulin therapy and if you're in Europe you might find the Dexcom One+ sensor to be more affordable than the G7 by the way. It's a 'cut down' version of the G7 - missing some features that are geared toward those on insulin therapy which a Type 2 who is not on insulin therapy probably doesn't need. Here in Ireland at least the One+ is much cheaper than the G7, it still allows for calibration like the G7 and has G7 levels of accuracy so it might be suitable for your needs too.

 

[p4ul]

I tend to see erratic readings like that when a lot of things are happening at once. Example - rushing to get to a morning doctors appointment: eat breakfast which causes a rise to begin after 20 to 30 minutes, have a hot shower which messes with the sensor readings temporarily due to rapid temperature changes, rush about trying to get ready to get out the door which might cause a change due to hormones (adrenaline and/or cortisol - 'fight or flight' and/or 'stress' hormones), walk to the doctor's office which will push levels down quickly following a meal due to the moderate exercise, then sit down in the waiting room which might cause another rise after the exercise if I'm still digesting my breakfast and carbs are still entering the bloodstream. The number of factors which can influence your blood glucose levels is very long.

Worth noting also though that sometimes the sensor just produces erratic readings, particularly in the first 24 hours and due to issues like 'compression lows' - pressure on the site where the sensor is placed will reduce circulation in the fatty tissue under the skin and cause low readings, which spring back up quickly when the pressure stops.

If you're not on insulin therapy and if you're in Europe you might find the Dexcom One+ sensor to be more affordable than the G7 by the way. It's a 'cut down' version of the G7 - missing some features that are geared toward those on insulin therapy which a Type 2 who is not on insulin therapy probably doesn't need. Here in Ireland at least the One+ is much cheaper than the G7, it still allows for calibration like the G7 and has G7 levels of accuracy so it might be suitable for your needs too.

One of the benefits of my G7 experiment is noticing what environmental factors can cause my BG to alter and I'm grateful for your confirmation on that.

Thanks also for the note on One+. I did dither a bit over which version to get but as a techy/data geek, I went for the G7 even though I'm T2. I'll give the One+ a go on my next purchase in 3 months.

 

[rebrascora]

I am guessing those variations are due to levels rising a bit and falling a bit as the different types of food release their glucose and your body tries to balance it with insulin and the CGM tries to keep up with those minor fluctuations. I don't see this sort of thing with Libre using the reader, it just redraws the graph when it has enough data to know what is going on, so that you get a smooth line that makes more sense.
It is important to understand that CGM tries to predict the current BG level from interstitial fluid readings by extrapolating the current trend but if levels have changed direction then it predicts higher or lower and then redraws when it has more data showing levels have changed, so if levels were rising and then started to fall or vice versa, it continues to predict the current trend until that change shows up in the interstitial fluid, which can mean that it is 20-30 mins behind when levels are changing but if levels are relatively stable then that extrapolation means that there is little or no lag and the sensor reading is more likely to be much closer to actual BG reading at that time.

 

[p4ul]

I am guessing those variations are due to levels rising a bit and falling a bit as the different types of food release their glucose and your body tries to balance it with insulin and the CGM tries to keep up with those minor fluctuations. I don't see this sort of thing with Libre using the reader, it just redraws the graph when it has enough data to know what is going on, so that you get a smooth line that makes more sense.
It is important to understand that CGM tries to predict the current BG level from interstitial fluid readings by extrapolating the current trend but if levels have changed direction then it predicts higher or lower and then redraws when it has more data showing levels have changed, so if levels were rising and then started to fall or vice versa, it continues to predict the current trend until that change shows up in the interstitial fluid, which can mean that it is 20-30 mins behind when levels are changing but if levels are relatively stable then that extrapolation means that there is little or no lag and the sensor reading is more likely to be much closer to actual BG reading at that time.

Fascinating background, thanks! I wonder if that's why there's a 3-hour lag before the G7 sends data to other apps? I did wonder.