Advice needed on HbA1c result and huge disparity with plasma result DEXCOM and finger prick average.

[Jan1956]

My HBA1C was 57 just over 3 months ago and I was diagnosed as T2
I have tried extremely hard to exercise & follow a careful low carb diet. My diet had been so low in carbs that sometimes I’ve been Keto.
I’ve lost 2 stone in weight and not far to go to target weight.
I’ve been Finger prick BG Testing and also have used a Dexcom monitor which I found highly accurate when comparing with finger prick test.
My monthly averages of Dexcom readings are 7.5 mmol/l
I’ve interpreted this 7.5 reading ( using the conversion table used in Diabetes .com ) as roughly a HBA1C of approx 58
2 months ago I had a fasting blood plasma test done and it read 7.5. So again fairly consistent with this.
So, today I received my HBA1C result and it’s 33 ??
While I’d like to rejoice at this great result I just feel it cannot be right???
A HBA1C suggests an average BG level of 5.2 and I’ve never, ever been this low?? Surely this cannot be right?
In none of my BG readings or Dexcom readings have I ever hit 5.2 Even during the night my readings are over 7 mmol/l
I keep wondering if I’ve got the correct result?
Could I have your thoughts ?
Thank you

 

[littlevoice359]

That middle graphic you attached to your post is what is causing the confusion, because you are looking at the same (7.5) value in two places, which are in entirely different units. As a result, you are essentially comparing apples and oranges.

Take a look at this link, which may clear things up for you: https://www.diabetes.org.uk/about-diabetes/looking-after-diabetes/hba1c

 

[Leadinglights]

I don't think that is the correct conversion chart as it is just converting the HbA1C result given in % which was the old units to mmol/mol not a conversion from mmol/l which is the units for blood glucose given by finger prick monitor or CGM.

 

[Jan1956]

That middle graphic you attached to your post is what is causing the confusion, because you are looking at the same (7.5) value in two places, which are in entirely different units. As a result, you are essentially comparing apples and oranges.

Take a look at this link, which may clear things up for you: https://www.diabetes.org.uk/about-diabetes/looking-after-diabetes/hba1c

@littlevoice359
Thank you for reply. So, to clarify , are you saying that when I’ve converted a 7.5 mmol/l BS average into a HBA1C conversion chart to reach a level of 57 this is wrong?
My thoughts are that to be getting a HBA1C result of 33 I should be hitting finger prick averages of 5.0 to 7.0 mmol/l. However, my readings haven’t budged at all. They are never ever, as low as this. They’re in their 10’s after meals and my morning fasting readings are always 8.5 mmol/l plus? This is why I can’t believe the HBA1C can be correct?

 

[Jan1956]

I don't think that is the correct conversion chart as it is just converting the HbA1C result given in % which was the old units to mmol/mol not a conversion from mmol/l which is the units for blood glucose given by finger prick monitor or CGM.

@Leadinglights
Ooh I’m so confused.
My BS readings havent budged since diagnosis. They’re all higher than they should be - they’re in their 8’s before eating and up to 12 or 13 sometimes after food. Even when I ate 6 cherries and an oat cracker they went up to 12?
This is why I’m so puzzled.
I know the Dr will be resistant to repeat the result.
Why I’m so doubtful is that I had a HBA1C blood test and a magnesium blood test at the same time and the HBA1C came back at 33 but the magnesium blood test appears to be “lost?”

 

[pjgtech]

My basic understanding is that there is no "direct" comparison of BG finger prick testing and 3 monthly HbA1c, you can use them as a very rough guide buts thats it. Plus the three monthly blood test is giving you a reading based on a three month average (sort of), and I think is generally regarded as being the more accurate reading, and the BG finger prick test and the Dexcom type monitors are not that accurate and can be a fair bit off.

 

[Docb]

Making sense of all the numbers can be a bit trying.

Of the data, the HbA1c result obtained from a test in an accredited laboratory from a blood sample taken from a vein is the one you can have the greatest confidence in. Not saying it cannot be wrong, just that the chances of that are very, very low.

I can see that your readings are not consistent with an Hba1c of 33 mmol/mol. You would expect average blood glucose from your CGM or finger pricker to be around 6 mmol/l and quite why yours seemingly not does seem to be a bit odd. How was your average calculated?

By the way, congratulations on losing 2 stone. Your reduced HbA1c is consistent with that!

 

[Leadinglights]

@Leadinglights
Ooh I’m so confused.
My BS readings havent budged since diagnosis. They’re all higher than they should be - they’re in their 8’s before eating and up to 12 or 13 sometimes after food. Even when I ate 6 cherries and an oat cracker they went up to 12?
This is why I’m so puzzled.
I know the Dr will be resistant to repeat the result.
Why I’m so doubtful is that I had a HBA1C blood test and a magnesium blood test at the same time and the HBA1C came back at 33 but the magnesium blood test appears to be “lost?”

The general rule of thumb is that if fasting /before meal readings are in the range 4-7 mmol/l and 2 hour post meal are below 8 mmol/l consistently for the 3 months prior to the test then your HbA1C would be expected to be in Normal range of below 42mmol/mol

 

[littlevoice359]

@littlevoice359
Thank you for reply. So, to clarify , are you saying that when I’ve converted a 7.5 mmol/l BS average into a HBA1C conversion chart to reach a level of 57 this is wrong?
My thoughts are that to be getting a HBA1C result of 33 I should be hitting finger prick averages of 5.0 to 7.0 mmol/l. However, my readings haven’t budged at all. They are never ever, as low as this. They’re in their 10’s after meals and my morning fasting readings are always 8.5 mmol/l plus? This is why I can’t believe the HBA1C can be correct?

I agree with you that the HbA1c result of 33 does seem inconsistent with your average readings. An average BG of 7.5 equates to an HbA1c of 48 (6.5%).

See attached graphic which illustrates the relationship between the different units.

Another thing I noticed in your post is that the Dexcom Clarity graphic shows average blood sugar over the past 30 days. You should really be looking at the 90 day average. Was your average BG markedly lower in the first 60 days of the current 90-day period?

 

[AndBreathe]

My HBA1C was 57 just over 3 months ago and I was diagnosed as T2
I have tried extremely hard to exercise & follow a careful low carb diet. My diet had been so low in carbs that sometimes I’ve been Keto.
I’ve lost 2 stone in weight and not far to go to target weight.
I’ve been Finger prick BG Testing and also have used a Dexcom monitor which I found highly accurate when comparing with finger prick test.
My monthly averages of Dexcom readings are 7.5 mmol/l
I’ve interpreted this 7.5 reading ( using the conversion table used in Diabetes .com ) as roughly a HBA1C of approx 58
2 months ago I had a fasting blood plasma test done and it read 7.5. So again fairly consistent with this.
So, today I received my HBA1C result and it’s 33 ??
While I’d like to rejoice at this great result I just feel it cannot be right???
A HBA1C suggests an average BG level of 5.2 and I’ve never, ever been this low?? Surely this cannot be right?
In none of my BG readings or Dexcom readings have I ever hit 5.2 Even during the night my readings are over 7 mmol/l
I keep wondering if I’ve got the correct result?
Could I have your thoughts ?
Thank you View attachment 32849

Jan, when I wear a Libre, it usually predicts an A1c of around 21, whereas my venous blood lab results serially return A1cs of 31-33.

I have come to accept that a CGM is about the traces and the trends in them, rather than the individual readings within it. Whilst my A1cs continue to run on the 31-33 tain-tracks I can't waste any more time querying it.

I see an ENdo for my thyroid, but he always touches on my diabetes, mainly, I think, because I've been in remission for a long time.

At the end of each appointment he warns me to keep a real eye on what's going on, because he reckons I'm sort of weird variant. I'm hoping to continue to prove him wring.

I'd urge to just try to maintain the tight control you current seem to have, but whilst living your life.

 

[Jan1956]

Making sense of all the numbers can be a bit trying.

Of the data, the HbA1c result obtained from a test in an accredited laboratory from a blood sample taken from a vein is the one you can have the greatest confidence in. Not saying it cannot be wrong, just that the chances of that are very, very low.

I can see that your readings are not consistent with an Hba1c of 33 mmol/mol. You would expect average blood glucose from your CGM or finger pricker to be around 6 mmol/l and quite why yours seemingly not does seem to be a bit odd. How was your average calculated?

By the way, congratulations on losing 2 stone. Your reduced HbA1c is consistent with that!

@Docb
Thank you!
My averages were collected from my DEXCOM average over the rolling months.
Also a separate average was taken from my finger prick readings - the finger prick readings only average the data of each prick but the DEXCOM readings are essentially averaged from the continuous data flow and should be more accurate .
This is what really puzzles me as the Dexcom readings are “spot on” with the finger prick readings when I’ve compared them and not a single one of my BG reading has ever been in the 5’s or 6’s over the last 3 months. It’s very strange to me.
I can’t quite understand this - it is a complete anomaly in my eyes.
I had two tests taken at the same time this week.
1) hba1c
2) magnesium
The path lab have lost the magnesium result and they sent the HBA1C result through on its own. I even keep wondering if it’s my result or a mistake.

 

[Jan1956]

I agree with you that the HbA1c result of 33 does seem inconsistent with your average readings. An average BG of 7.5 equates to an HbA1c of 48 (6.5%).

See attached graphic which illustrates the relationship between the different units.

Another thing I noticed in your post is that the Dexcom Clarity graphic shows average blood sugar over the past 30 days. You should really be looking at the 90 day average. Was your average BG markedly lower in the first 60 days of the current 90-day period?

@littlevoice359
Thank you for the graph. I have copied this for my future reference.
The DEXCOM average was for the latter part of the period as I was initially using a libre freestyle.
The libre did average lower than Dexcom for the first two months but I felt the libre was way out and not consistent with my finger prick readings. The finger prick readings have barely changed throughout the 3 months. I record morning fasting. Before a meal and two hours afterwards. The morning fasting is around 8.5. Initially in the 9’s. Before meals is around 7.5 to 8.5 and after meals 2 hrs is between 8.5 and 10

 

[Leadinglights]

You mention you were tested for magnesium level, why was that?
Those finger prick reading do not seem consistent with an HbA1C as low as 33mmol/mol.
I should point this out and ask for a repeat at the same time as they will presumably need to repeat the magnesium test as it was lost.

 

[Jan1956]

Jan, when I wear a Libre, it usually predicts an A1c of around 21, whereas my venous blood lab results serially return A1cs of 31-33.

I have come to accept that a CGM is about the traces and the trends in them, rather than the individual readings within it. Whilst my A1cs continue to run on the 31-33 tain-tracks I can't waste any more time querying it.

I see an ENdo for my thyroid, but he always touches on my diabetes, mainly, I think, because I've been in remission for a long time.

At the end of each appointment he warns me to keep a real eye on what's going on, because he reckons I'm sort of weird variant. I'm hoping to continue to prove him wring.

I'd urge to just try to maintain the tight control you current seem to have, but whilst living your life.

@AndBreathe
Thank you.
My libre results were considerably lower than Dexcom and weren’t consistent with my finger prick tests at all. Way out in fact.
Perhaps I am a bit of an anomaly like you? My instincts are that my diabetes is definitely not as clear cut as my recent result indicates. If I take consideration to my latest finger prick readings they are still of concern as they are way too high despite my result.
Can I ask you if your finger prick readings are an accurate reflection of your HBA1C? Or are they much higher like mine?
It surely is mystery and I’ve even wondered whether I should be asking my GP for a referral to a diabetes specialist. However I can imagine the GP response with such a good HBA1C as mine is currently. I will just be labelled as an over worrier! Which I don’t think I actually am!

 

[Jan1956]

You mention you were tested for magnesium level, why was that?
Those finger prick reading do not seem consistent with an HbA1C as low as 33mmol/mol.
I should point this out and ask for a repeat at the same time as they will presumably need to repeat the magnesium test as it was lost.

@Leadinglights
The magnesium test was re ordered because my electrolyte level is too low and low magnesium is dangerous.- I have IBS and this can cause low magnesium if it’s severe in terms of bowel issues.i will be asking for a repeat magnesium. This should be ok.
Re asking for a repeat HBA1C test - it’s unlikely it will be agreed. When I was initially diagnosed the dr agreed to retest after 2 months as a reassurance and I went for a test but the path lab refused to do the repeat test saying that it could only be repeated at a minimum of 3 months.
Hence in my results list above you will see a gap with no result - this is where they refused to retest.

 

[Leadinglights]

@Leadinglights
The magnesium test was re ordered because my electrolyte level is too low and low magnesium is dangerous.- I have IBS and this can cause low magnesium if it’s severe in terms of bowel issues.i will be asking for a repeat magnesium. This should be ok.
Re asking for a repeat HBA1C test - it’s unlikely it will be agreed. When I was initially diagnosed the dr agreed to retest after 2 months as a reassurance and I went for a test but the path lab refused to do the repeat test saying that it could only be repeated at a minimum of 3 months.
Hence in my results list above you will see a gap with no result - this is where they refused to retest.

They say 3 months because that is the approximate life of your red blood cells so it needs to wait for all the 'old' cells to have been replaced to reflect the previous 3 months.
If you explain to possible error and discrepancy between that and your blood glucose readings they may relent and agree to a repeat test.
Some pharmacies are offering an HbA1C which a few people have used and found them (much to my surprise) pretty close to their official HbA1C. Obviously you would need to pay but may be worth it to put your mind at rest.
However if you are convinced your finger prick and Dexcom data are the more accurate then given they are higher than desirable then taking some action to try to reduce your readings would be beneficial.

 

[Lucyr]

A HBA1C suggests an average BG level of 5.2

No it doesn’t. You’ve taken a conversion chart between hba1c in % and in mmol/mol and assumed it means average fingerprick reading. It doesn’t. Hba1c is a totally seperate measure to fingerprick glucose readings, you can only compare each method to itself. If your a1c is lower than previous ones then you’re improving, that’s all it tells you really.

 

[AndBreathe]

@AndBreathe
Thank you.
My libre results were considerably lower than Dexcom and weren’t consistent with my finger prick tests at all. Way out in fact.
Perhaps I am a bit of an anomaly like you? My instincts are that my diabetes is definitely not as clear cut as my recent result indicates. If I take consideration to my latest finger prick readings they are still of concern as they are way too high despite my result.
Can I ask you if your finger prick readings are an accurate reflection of your HBA1C? Or are they much higher like mine?
It surely is mystery and I’ve even wondered whether I should be asking my GP for a referral to a diabetes specialist. However I can imagine the GP response with such a good HBA1C as mine is currently. I will just be labelled as an over worrier! Which I don’t think I actually am!

Eleven years in remission I test much less than I used to, but fingerprick testing is a bit of an otters anyway. Whatever the number reads, it could be rising rapidly, falling rapidly or any point between. It’s a reading at the snap of the fingers.

I’d be astonished if your GP referred you to clinic with the history and numbers you have. T1 appointments are not taking place as they should be

My knee jerk reaction is grind out a few more A1c cycles, then consider again. Even if your GP agrees to fill out the forms, there is a clinic triage, and referrals can be rejected at that stage.

My Endo referral was vpnever for diabetes. It was and is to help with my errant thyroid condition. I initially saw him is his private clinic, but on the first appointment it was clear my thyroid was and is seriously off it’s game, even with very highly levels of the medications GPs can prescribe. My diabetes was an “interesting” “side show”, along the lines of why was your A1c 73 then 4 months later 37 (then onto the 31-33 tracks).

I had lost a bit of weight, cut carbs in a guided way, by finger prick testing. Libre didn’t exist at all. And I had undertaken a long and active sailing trip.

For me, that’s great, but not black magic; improving diet, moving much more (with less stress) and trimming up is now a much more accepted positive formula

 

[Jan1956]

They say 3 months because that is the approximate life of your red blood cells so it needs to wait for all the 'old' cells to have been replaced to reflect the previous 3 months.
If you explain to possible error and discrepancy between that and your blood glucose readings they may relent and agree to a repeat test.
Some pharmacies are offering an HbA1C which a few people have used and found them (much to my surprise) pretty close to their official HbA1C. Obviously you would need to pay but may be worth it to put your mind at rest.
However if you are convinced your finger prick and Dexcom data are the more accurate then given they are higher than desirable then taking some action to try to reduce your readings would be beneficial.

@Leadinglights
Thank you for the advice. I’m going to book a GP appt . to discuss the results. I was wondering also about paying privately for a test but wasn’t sure how accurate they might be.
I’ve just done further Dr google search and there are thoughts that HBA1C may be inaccurate in certain instances. Suggestions are to follow up with fasting glucose test and glucose tolerance test to confirm so I will politely suggest my thoughts on this to the gp and see where it takes me.
Thank you.

 

[JITR]

@Jan1956

Before you ask your GP's advice I suggest you listen to Professor Elizabeth Selvin in this podcast, starting at 17.23 minutes: 17:32: Alice interviews Dr. Elizabeth Selvin, author of a Perspectives in Care called “The Glucose Management Indicator: Time to Change Course?” This study is also an editor-selected feature article in the June 2024 issue and is openly accessible at https://doi.org/10.2337/dci23-0086.

She says, Glucose Management Indicator (GMI) and HbA1c do not 'line up very well' and when they don't 'you won't know why'.

Also have a look at the article she is discussing in the podcast (link quoted above, graphical abstract below):