CGM says glucose high, meter reading says glucose low

[SWAN2019]

Wondering if anyone else has come across this. Last week during a particularly stressful day my CGM was giving high readings and for a while would not even scan and a bit of data lost. But think at this time it possibly peaked at around 21. It stayed high for many hours. At one point the CGM reading when it was around 13 I checked it against the blood glucose meter and that was saying 3.9. I checked it a few more times and the difference was substantial all the time. I was feeling really rubbish so also checked ketones which with a urine test was at 4. I hadn't had much to eat and drink which probably was part of the reason but still be good to understand why the two readings were so different. My only conclusion is that the sugar that was in my system had moved into the fluid surrounding the cells but for some reason, maybe due to dehydration or stress was not moving into the cells, hence low blood sugar reading but high CGM reading. Body may then have used fat for energy hence the high ketone levels. After taking on more fluid the ketone levels did start to drop.

 

[rebrascora]

Hi

Which CGM are you using and which BG meter?

Generally we suggest that a finger prick reading is likely to be more reliable than CGM but there are a couple of the cheaper BG meters which give a false low reading if you don't get enough blood for the test strip, rather than giving an error code which would alert you to the test not working correctly.

Whilst being dehydrated will often cause the CGM to give a higher reading than a finger prick, we are talking 2-4 mmols not 10-15mmols higher so I would strongly suspect one of your devices is not giving correct data and I am suspicious of the BG meter reading, because a low reading would be unlikely if you are diabetic and you are stressed.
In your situation, I would repeat the finger prick test being careful to hold your finger steady when applying the blood to the test strip. If finger prick is more in line with the CGM and double checking the ketones still gives a high reading, then I think I would contact 111 or go to A&E. Actually I would inject insulin, but I am not sure if you have that option.

Which medication(s) are you taking for your diabetes?

 

[Inka]

Your older posts say you were concerned you might be Type 1/LADA @SWAN2019 Has that been ruled out now? Like @rebrascora i’d ask what glucose meter you’re using. Usually you’d go by the meter not the CGM, but if you have a rubbishy meter then that would make a difference. Stress can definitely cause high blood sugars. Usually the CGM will read a bit higher than you actually are,but there wouldn’t be such a huge difference between the two unless one was faulty.

 

[everydayupsanddowns]

Sorry you’ve had some fairly extreme differences between fingerstick and CGM levels.

They are amazing bits of kit, but they can go wrong from time to time, and both are capable of giving duff data under different circumstances.

It might be worth contacting the sensor manufacturer and asking for a replacement?

I’m a little concerned about the combination of high BGs and ketones you had - perhaps its worth booking an appointment with your GP to discuss things, expecially if there were some doubts over your diabetes classification?

 

[SWAN2019]

Hi

Which CGM are you using and which BG meter?

Generally we suggest that a finger prick reading is likely to be more reliable than CGM but there are a couple of the cheaper BG meters which give a false low reading if you don't get enough blood for the test strip, rather than giving an error code which would alert you to the test not working correctly.

Whilst being dehydrated will often cause the CGM to give a higher reading than a finger prick, we are talking 2-4 mmols not 10-15mmols higher so I would strongly suspect one of your devices is not giving correct data and I am suspicious of the BG meter reading, because a low reading would be unlikely if you are diabetic and you are stressed.
In your situation, I would repeat the finger prick test being careful to hold your finger steady when applying the blood to the test strip. If finger prick is more in line with the CGM and double checking the ketones still gives a high reading, then I think I would contact 111 or go to A&E. Actually I would inject insulin, but I am not sure if you have that option.

Which medication(s) are you taking for your diabetes?

Hi

I have the Libre Freestyle 2 and True Metrix Meter. Most the time they are similar but I had checked blood glucose a couple of times during that day and the results were quite different. Later they were similar.

I only have Metformin as medication

 

[SWAN2019]

Your older posts say you were concerned you might be Type 1/LADA @SWAN2019 Has that been ruled out now? Like @rebrascora i’d ask what glucose meter you’re using. Usually you’d go by the meter not the CGM, but if you have a rubbishy meter then that would make a difference. Stress can definitely cause high blood sugars. Usually the CGM will read a bit higher than you actually are,but there wouldn’t be such a huge difference between the two unless one was faulty.

Hi

As far as the doctors are concerned I am type 2. It has only taken me 20 months to finally get them to let me go on one of the diabetes education courses! Getting anything done at my surgery is a challenge and different people give you diferent diets depending on blood test results and they contradict each other.

The meter is the True Metrix one which are pretty good, carried by a number of airlines as they are compact and simple to use, and they do show up errors if not a big enough sample of blood, etc. Later on they settled down to be similar

 

[SWAN2019]

Sorry you’ve had some fairly extreme differences between fingerstick and CGM levels.

They are amazing bits of kit, but they can go wrong from time to time, and both are capable of giving duff data under different circumstances.

It might be worth contacting the sensor manufacturer and asking for a replacement?

I’m a little concerned about the combination of high BGs and ketones you had - perhaps its worth booking an appointment with your GP to discuss things, expecially if there were some doubts over your diabetes classification?

Thanks for reply. I have finally been able to get on a diabetes education course, no idea why this wasn't done initially, instead of 2 useless appointments with the diabetic nurse. I am hoping it gives me a chance to ask some questions from people who have had a bit more training than the diabetic nurse. In the meantime I am keeping an eye on the ketones but no issues since that day.

 

[trophywench]

I reckon you were pretty dehydrated - so let that be a warning not to get dehydrated - this weather we absolutely do need to drink a lot more fluids, and tap water is our friend usually!

 

[SWAN2019]

I reckon you were pretty dehydrated - so let that be a warning not to get dehydrated - this weather we absolutely do need to drink a lot more fluids, and tap water is our friend usually!

That is my conclusion, although where I live the tap water is awful! Like drinking a bottle of bleach

 

[Leadinglights]

That is my conclusion, although where I live the tap water is awful! Like drinking a bottle of bleach

If you leave the water in the fridge the chlorine should dissipate or you could get a water filter or buy some bottled water still or sparkling. Pretty cheap from somewhere like Costco. A small amount of sugarfree cordial and a slice of lemon may help.