How can I rely on my glucose monitor?

[Allell]

I discovered in august that I was pre-diabetic (hospital fasting test 6.7). Since then I’ve worked hard to turn this around. I’ve lost 2 and I’m on about 40-50g carbs a day. I bought a monitor and have tested fasting glucose once a week. Results have been between 4.8 and 6.2. Last mon I had a hospital test booked so I checked on my own monitor 15 mins before my test and got a reading of 3.7 ( lowest I’ve had). Just had results from hospital and they were 5.2. It’s such a big difference I don’t know how I can rely on my monitor in the future if I want to check the impact certain foods have on me. Has anyone else had this problem?

 

[Lakeslover]

Firstly I just wanted to check that the hospital reading was blood sugar, not Hba1c which would be expected to give a different result.

assuming it is I don’t think there is anything to be worried about. All meters operate within a margin of accuracy and therefore the 3.7 could actually have been anywhere up to mid 4. But also what were you doing in those 15 minutes. If you walked anywhere your blood sugar may rise, if your body was nervous about the blood being taken, or getting there on time, or parking the car etc your liver will release sugar into your blood in preparation for a “fight or flight” response. Finally I wear a libre sensor. Sitting here in my chair, fasting (nothing to eat for 14 hours), reading posts, doing nothing, my blood sugar has risen nearly 1 point in the last 15 minutes.

finally congratulations on that 5.2. A normal result which shows the benefit of your hard work. Keep it up, you must be doing the right things!

 

[bulkbiker]

I checked on my own monitor 15 mins before my test and got a reading of 3.7 ( lowest I’ve had). Just had results from hospital and they were 5.2.

Could well be stress related.. going to the hospital very likely to have caused a blood glucose release?

Did they just take a finger prick at the hospital or are you talking about another test?
If it was a finger prick why did you have to wait for the result?

 

[KK123]

I discovered in august that I was pre-diabetic (hospital fasting test 6.7). Since then I’ve worked hard to turn this around. I’ve lost 2 and I’m on about 40-50g carbs a day. I bought a monitor and have tested fasting glucose once a week. Results have been between 4.8 and 6.2. Last mon I had a hospital test booked so I checked on my own monitor 15 mins before my test and got a reading of 3.7 ( lowest I’ve had). Just had results from hospital and they were 5.2. It’s such a big difference I don’t know how I can rely on my monitor in the future if I want to check the impact certain foods have on me. Has anyone else had this problem?

Hi there, first off, it's not a big difference, it's a difference of 1.5 which is just about deemed within the margin of accuracy as mentioned. Also, as others have said, that 15 minutes wait can make a very significant difference, I can take mine say at 6, and 15 minutes later it can easily be up at 8 plus or down at 4 plus. Stress, worry, or just running up the stairs can do it, it could be that your body thought its 3.7 was too low or going lower and helpfully gave you a shot of glucose to bring it up to 5 which is a perfectly acceptable reading anyway. I think people can easily make the mistake of thinking that the glucometers are able to give a 100% accuracy reading, but in reality it is nowhere near and it's only giving you the measurement at that precise time. Same with the Libres et al. Try using your meter to take 2 readings from the same finger at the same time and you may well get different readings of around 1 to 1.5 difference. It's not great but it's certainly good enough to be able to use it to see those foods that will raise you, if you eat a food that is too high in carbs for your body to cope with, that '1.5' difference will hardly come into it, you would see it shoot up well beyond your average/normal readings, or hardly at all if your body was coping with the carbs. A Libre or CGM, takes the readings every 15 minutes or continuously and it shows in detail the ups and downs of glucose 24/7, like many other functions of our bodies it does not remain at the same number, it fluctuates. I really don't think it's a problem, it's just that the glucometers have limitations. I (as with any insulin users) have to rely on it for dosage and it's deemed accurate enough for that so you should be fine.

 

[Jaylee]

I discovered in august that I was pre-diabetic (hospital fasting test 6.7). Since then I’ve worked hard to turn this around. I’ve lost 2 and I’m on about 40-50g carbs a day. I bought a monitor and have tested fasting glucose once a week. Results have been between 4.8 and 6.2. Last mon I had a hospital test booked so I checked on my own monitor 15 mins before my test and got a reading of 3.7 ( lowest I’ve had). Just had results from hospital and they were 5.2. It’s such a big difference I don’t know how I can rely on my monitor in the future if I want to check the impact certain foods have on me. Has anyone else had this problem?

Hi,

The result of "5.2" From the hospital test. Could it have been from blood drawn from the arm & sent to a lab?

 

[Bubbleblower]

May be EllieM can tell you how you can rely more on your monitor.

HbA1c isn't nessecarily reliable either, in some labs it can be off by 20% (!)

 

[Mr_Pot]

May be EllieM can tell you how you can rely more on your monitor.

HbA1c isn't nessecarily reliable either, in some labs it can be off by 20% (!)

View attachment 52307

That's probably informative if only I knew what it meant. Do you have some text to go with it?

 

[searley]

In short you can test on 1 hand.. and get a similar difference testing on the other hand right away

Home meters are not lab grade... and have a margin or error

 

[Jaylee]

In short you can test on 1 hand.. and get a similar difference testing on the other hand right away

Home meters are not lab grade... and have a margin or error

Hi,
I wouldn't dissagree.

From what I've read & come to understand BG level concentrations arn't even consistent throughout the whole body?
Blood flow. (Let alone the tolerance of 15%?)
They are a guide as opposed to "gospel." That's my take on it after 45.5 year of BG watching 8 of which was either peeing in tha test tube or on a stick..?

However, meter's are informative to things going awry.. (Or not.)

 

[Riva_Roxaban]

However, meter's are informative to things going awry.. (Or not.)

They are if you test more than once a week as the OP @Allell is doing at present.

The more tests per day you do the more data you collect.

 

[Bubbleblower]

That's probably informative if only I knew what it meant. Do you have some text to go with it?

Here you go:

“Impact of bias and imprecision on the clinical interpretation of a sample with an HbA1c of 43 mmol/mol (6.1%). The impact of a bias of 5 mmol/mol (0.46%) is shown on the left. The impact of several levels of imprecision is shown on the right” Based on data of 125 individual laboratories.

But you'll find this more interesting:

“In Birmingham, UK, 1457 patients with impaired fasting glucose (6.1 to 6.9 mmol/L) were
referred by their family doctors for OGTT for diagnosis of diabetes with HbA1c measured on a
Tosoh G8 analyser at the diabetes centre”

“The offsets observed for particular HbA1c assays studied would result in different proportions
of people being diagnosed with diabetes depending on the assay used. Translation of the positive biases observed in this study performed between 2007 and 2010 down to IFCC SRM HbA1c values in two populations presenting for OGTT would result in a lowering of the prevalence of diabetes by approximately one third i.e. from 36% to 22% for HbA1c results obtained using a Tosoh G8 analyser in Birmingham, UK”

Comparison of IFCC-calibrated HbA1c from Laboratory and Point of Care Testing System


Glucose meters should be within ±15% according to ISO standards, but IRL they are not, studies found differences up to 43% and 44% respectively. My first meter was even worse with a huge positive bias, which took me several months to find out. So I bought a second meter which turned out to have a big negative bias. Since these meters are almost free with these starters packages I got me a third one which has almost no bias at all. So you need to be lucky with these meters.

 

[Allell]

Firstly I just wanted to check that the hospital reading was blood sugar, not Hba1c which would be expected to give a different result.

assuming it is I don’t think there is anything to be worried about. All meters operate within a margin of accuracy and therefore the 3.7 could actually have been anywhere up to mid 4. But also what were you doing in those 15 minutes. If you walked anywhere your blood sugar may rise, if your body was nervous about the blood being taken, or getting there on time, or parking the car etc your liver will release sugar into your blood in preparation for a “fight or flight” response. Finally I wear a libre sensor. Sitting here in my chair, fasting (nothing to eat for 14 hours), reading posts, doing nothing, my blood sugar has risen nearly 1 point in the last 15 minutes.

finally congratulations on that 5.2. A normal result which shows the benefit of your hard work. Keep it up, you must be doing the right things!

Thank you, that makes sense. I was a bit anxious about hospital yesterday as they always struggle to get my blood out! It was just a fasting test. They were supposed to check HBA1C too but didn’t process it so I have to go back!

 

[Allell]

Could well be stress related.. going to the hospital very likely to have caused a blood glucose release?

Did they just take a finger prick at the hospital or are you talking about another test?
If it was a finger prick why did you have to wait for the result?

It was a test they sent to the lab

 

[Allell]

Hi there, first off, it's not a big difference, it's a difference of 1.5 which is just about deemed within the margin of accuracy as mentioned. Also, as others have said, that 15 minutes wait can make a very significant difference, I can take mine say at 6, and 15 minutes later it can easily be up at 8 plus or down at 4 plus. Stress, worry, or just running up the stairs can do it, it could be that your body thought its 3.7 was too low or going lower and helpfully gave you a shot of glucose to bring it up to 5 which is a perfectly acceptable reading anyway. I think people can easily make the mistake of thinking that the glucometers are able to give a 100% accuracy reading, but in reality it is nowhere near and it's only giving you the measurement at that precise time. Same with the Libres et al. Try using your meter to take 2 readings from the same finger at the same time and you may well get different readings of around 1 to 1.5 difference. It's not great but it's certainly good enough to be able to use it to see those foods that will raise you, if you eat a food that is too high in carbs for your body to cope with, that '1.5' difference will hardly come into it, you would see it shoot up well beyond your average/normal readings, or hardly at all if your body was coping with the carbs. A Libre or CGM, takes the readings every 15 minutes or continuously and it shows in detail the ups and downs of glucose 24/7, like many other functions of our bodies it does not remain at the same number, it fluctuates. I really don't think it's a problem, it's just that the glucometers have limitations. I (as with any insulin users) have to rely on it for dosage and it's deemed accurate enough for that so you should be fine.

That’s interesting. Didn’t realise it could vary that much in just 15 mins.

 

[Allell]

Hi,

The result of "5.2" From the hospital test. Could it have been from blood drawn from the arm & sent to a lab?

Yes it was a lab test.

 

[bulkbiker]

It was a test they sent to the lab

So it wasn't simply measuring the finger prick test and it might have been an HbA1c which has different units to a finger prick?

Do you have the results with the units that were being measured then we can help uncover the mystery.

 

[Jaylee]

Yes it was a lab test.

Hi,

Then it sounds like your HbA1c test, which gives an average BG levels over the past 3 month period.
Finger testing with a meter once a week will not reflect regarding the A1c. It just tells you what they were in the last 15/20 minutes at that point in time.?

 

[Allell]

So it wasn't simply measuring the finger prick test and it might have been an HbA1c which has different units to a finger prick?

Do you have the results with the units that were being measured then we can help uncover the mystery.

It was just a fasting glucose test not HBA1C

 

[bulkbiker]

It was just a fasting glucose test not HBA1C

A fasting glucose would be a finger prick surely?
I've never had a fasting glucose test sent off to a lab only HbA1c.
Did they draw blood into a vial?

 

[jape]

A fasting glucose would be a finger prick surely?
I've never had a fasting glucose test sent off to a lab only HbA1c.
Did they draw blood into a vial?

Maybe we do things differently here in Canada, but every time I go for blood work, the battery of tests includes both fasting BG, as well as a1c. I always wonder why the doctor requests both tests, as the fasting BG can easily be manipulated, such as me giving me a fast working insulin injection an hour before blood is being drawn, thus being a waste of money.