Listlad
BANNED
- Messages
- 3,971
- Type of diabetes
- Prediabetes
- Treatment type
- Diet only
Can you be sure of catching the peak from a one off meter reading? Might it have passed you by altogether?
-
Guest - w'd love to know what you think about the forum! Take the 2025 Survey »
Control solution...who knew? Meter vs Labs
- Thread starter zauberflote
- Start Date
Obviously not.. the absolute value of the "peak" is irrelevant in itself.. that there has been a spike is what is relevant.
Listlad
BANNED
- Messages
- 3,971
- Type of diabetes
- Prediabetes
- Treatment type
- Diet only
Yes, but will you always catch that spike?
How fast do you think your blood sugars react to food? If you are really keen on the spike you could test every 15 minutes after eating and watch it in "real time" then you'll know.. I only did this when I did my home OGTT.
Got this graph
x axis is minutes..
ziggy_w
Well-Known Member
Hello all,
I had a similar problem as @zauberflote. So, I can definitely empathize. Expected an HbA1c of 28 (4.8%) based on meter readings (average of 5.0 mmol or 90mg/dl) in September last year and got an HbA1c of 36 (5.4%) (average 6.0 or 108 mg/dl) -- so an 8 point difference between expected and actual HbA1c).
Subsequently, I put quite a lot of research into the subject matter to try to figure out why I might see this difference.
One importance assumption on which the HbA1c rests is that red blood cells survive the same length of time in all people all of the time. However, this assumption doesn't necessarily seem to hold. There are differences between individual in this respect and also diffeences within the same person. For example, due to glucotoxicity, red blood cells generally don't survive as long when blood sugars are high, thus HbA1c tends to underestimate average blood glucose in this case.
For the geeks among us, here are some sources which discuss the issue with lab-based HbA1c, some comparing it to readings by continuous glucose monitoring:
https://chriskresser.com/why-hemoglobin-a1c-is-not-a-reliable-marker/
https://www.liebertpub.com/doi/pdfplus/10.1089/dia.2013.0224
https://www.diabetes.co.uk/news/201...-red-blood-cell-age-variability-91218453.html
The last of these sources states that HbA1c can be as much as 15 mg/dl (0.8 mmol) off, which in my case might almost be able to explain the entire difference between between expected and actual HbA1c. So, based on this, I'd definitely go with the meter over an HbA1c test.
Another reasons for this (apart from the literature) is that I tested my meter twice against lab values. The first time, meter reading was 77 mg/dl (4.3 mmol) before test, then meeting with GP and after getting out of lab tests it was 84 mg/dl (4.7 mmol), lab test was 82 mg/dl (4.6 mmol). The second time, meter reading right before the lab test was 80 mg/dl (4.4 mmol) and lab test reading was exactly 80 mg/dl (4.4 mmol) -- so based on this I concluded my meter is reasonably accurate.
Then I took readings every half hour (after meals even more often) for three days trying to catch all peaks (after food and after exercise). The difference in readings including all the peaks was about 3 mg/dl (0.2 mmol) -- so, this would be a difference of 0.1% or about 1 mmol in HbA1c, but fails explain the 8 mmol difference. In addition, (if I remember correctly) Jenny Ruhl (Bloodsugar 101) reports that if blood sugars are elevated for less than two hours, sugar detaches again from red blood cells, thus not affecting HbA1c.
I even tested several times at night because my GP suggested that the discrepancy might be caused by higher overnight readings (though they would have to be on average 160 mg/dl or 8.9 mmol while I sleep to account for the difference, which is btw a level I never see). Of course testing showed no elevation at night.
So other than wearing a Dexcom G6 (which at 400 Euros a month, I can't afford), I have done all I can think of to get to the root cause of this discrepancy.
Sorry for the extremely long post, just wanted to explain why I trust my meter readings more than the lab-based HbA1c.
I had a similar problem as @zauberflote. So, I can definitely empathize. Expected an HbA1c of 28 (4.8%) based on meter readings (average of 5.0 mmol or 90mg/dl) in September last year and got an HbA1c of 36 (5.4%) (average 6.0 or 108 mg/dl) -- so an 8 point difference between expected and actual HbA1c).
Subsequently, I put quite a lot of research into the subject matter to try to figure out why I might see this difference.
One importance assumption on which the HbA1c rests is that red blood cells survive the same length of time in all people all of the time. However, this assumption doesn't necessarily seem to hold. There are differences between individual in this respect and also diffeences within the same person. For example, due to glucotoxicity, red blood cells generally don't survive as long when blood sugars are high, thus HbA1c tends to underestimate average blood glucose in this case.
For the geeks among us, here are some sources which discuss the issue with lab-based HbA1c, some comparing it to readings by continuous glucose monitoring:
https://chriskresser.com/why-hemoglobin-a1c-is-not-a-reliable-marker/
https://www.liebertpub.com/doi/pdfplus/10.1089/dia.2013.0224
https://www.diabetes.co.uk/news/201...-red-blood-cell-age-variability-91218453.html
The last of these sources states that HbA1c can be as much as 15 mg/dl (0.8 mmol) off, which in my case might almost be able to explain the entire difference between between expected and actual HbA1c. So, based on this, I'd definitely go with the meter over an HbA1c test.
Another reasons for this (apart from the literature) is that I tested my meter twice against lab values. The first time, meter reading was 77 mg/dl (4.3 mmol) before test, then meeting with GP and after getting out of lab tests it was 84 mg/dl (4.7 mmol), lab test was 82 mg/dl (4.6 mmol). The second time, meter reading right before the lab test was 80 mg/dl (4.4 mmol) and lab test reading was exactly 80 mg/dl (4.4 mmol) -- so based on this I concluded my meter is reasonably accurate.
Then I took readings every half hour (after meals even more often) for three days trying to catch all peaks (after food and after exercise). The difference in readings including all the peaks was about 3 mg/dl (0.2 mmol) -- so, this would be a difference of 0.1% or about 1 mmol in HbA1c, but fails explain the 8 mmol difference. In addition, (if I remember correctly) Jenny Ruhl (Bloodsugar 101) reports that if blood sugars are elevated for less than two hours, sugar detaches again from red blood cells, thus not affecting HbA1c.
I even tested several times at night because my GP suggested that the discrepancy might be caused by higher overnight readings (though they would have to be on average 160 mg/dl or 8.9 mmol while I sleep to account for the difference, which is btw a level I never see). Of course testing showed no elevation at night.
So other than wearing a Dexcom G6 (which at 400 Euros a month, I can't afford), I have done all I can think of to get to the root cause of this discrepancy.
Sorry for the extremely long post, just wanted to explain why I trust my meter readings more than the lab-based HbA1c.
Last edited:
Listlad
BANNED
- Messages
- 3,971
- Type of diabetes
- Prediabetes
- Treatment type
- Diet only
Got it.
britishpub
Well-Known Member
Is it just a coincidence that the only people who distrust their HbA1c are those who get a higher result than they calculate from their couple of finger prick tests a day?
It's also weird how nobody seems to distrust a HbA1c test as a way of diagnosing their T2D.
Bonkers x2
The range is set to 4 to 8, when a 5 min reading is below that, it's a red dot, in range is blue and above is yellow, so the yellow curve is it going from 8 up to 12 and then back down to below 8 about 3 hrs later.
Listlad
BANNED
- Messages
- 3,971
- Type of diabetes
- Prediabetes
- Treatment type
- Diet only
Got that. But what was the cause of the peak? A full blown meal?
ziggy_w
Well-Known Member
Honestly, if my HbA1c was exactly what I expected it to be, why would I distrust it. You might also ask the question the other way around, why is it all those that get an HbA1c in the expected range think that it is accurate? Alternatively, we might also ask why is it always people who are not metabolically challenged who doubt that carbs are a problem if you're insulin-resistant?
Why don't we just settle at where we usually do, that we are all different. For some of us, it may be accurate, for some us not so much. (Btw, this is also seems to be what the research shows.)
As to your second point - at diagnosis, my HbA1c was 100, so even if it was a bit off then (and research seems to indicate, it was likely higher than this), there would be no way to deny that it was most definitely diabetic. However, at much lower levels (let's say somewhere in the range of 42 to 48, or maybe even 50) I would most definitely question it.)
Last edited:
Basically too little insulin taken too close to first bite.
Because I'd been low, I'd nudged up with 10g dextrotabs and then had 7u for a 75g meal but only about 10 mins before to reduce the chances of a further drop but obviously overdid the precautions.
Compare that to the first graph where I'm having 13u about 25 mins before a 95g meal and the level barely shifts.
