ziggy_w
Well-Known Member
- Messages
- 3,019
- Type of diabetes
- Type 2
- Treatment type
- Diet only
Hi ziggy_w
thanks a lot. This is very useful.
Do I understand that CGMs are the metres, e.g. Dexcom G6, which measure just beneath your skin?
For illustration Hb1Ac measurement of 53 mmol/l corresponds to a CGM of 160 mg/dl on average.
The plot contains 95% intervals, but even if I eyeball a 67% interval (1 standard deviation)
you can get a variation of Hb1Ac values about 6 values up to 59 and down to 47 which also will
give CGM of 160. This is quite scary for two reasons.
1) When people fret about being below the diabetes threshold of 42, they could be off by a huge margin.
2) I would be surprised if all GPs know that there can be such large discrepancies between Hb1Ac and CGM.
I also read that for individuals the Hb1Ac variation is much more stable.
Thus I have to accept that for me the rise from 42 to 55 is real. Maybe Christmas where I did not resist sweets (which I usually do) and also not fast had a bigger impact on my Hb1Ac.
Hi @Lupf,
Yes, I agree. I doubt many people realize there is quite a large margin of error for individuals.
The reason I looked into this that about one and half years ago, my HbA1c was about 6 mmol higher than anticipated based on finger pricks (and I did quite a lot of finger pricks, so doubt I missed much). My GP suggested that maybe blood sugars were elevated during sleep. I calculated that my blood sugars must have been 8.9 mmol on average at night compared to 5.1 average during the day to arrive at this average, which did not sound likely to me. This was also confirmed when setting my alarm clock at night to check and blood sugars and they were pretty much the same as fasting values during the day -- so no rise during the night.
Anyway when I next met with my GP, I brought some printout of the research. You are right, he had no idea that HbA1c could be off by so much.
Just eyebaling the graph, I would say the one standard deviation is about 15 mg/dl. So, if about 65% of the people are within plus/minus one standard deviation of the mean -- with an HbA1c of 5.0% (or 31 mmol), the "real" (i.e. observed) HbA1c could range from 4.5% (26 mmol) and 5.5% (37mmol). For the remaining 35% of the people, this variation would even be larger (hope my math is correct).
So, with a reading of 42 mmol, you could in reality be either non-diabetic, prediabetic or fully diabetic.
So based on this, I agree with @Mbaker and trust my meter readings more than the HbA1c as I also tested it against lab values and it is quite accurate. Wished I could afford a CGM though.
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