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Correlation in between HbA1c and Blood sugar readings taken at home

Kaha

Kaha

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Canada
Type of diabetes
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Tablets (oral)
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I am requesting the experienced forum members views on the subject above.
I am a T2 since 2005 on medication.
I had recorded blood sugar readings taken at home those were taken on a regular interval and at different times of the day . For the period from mid June 2014 to Mid September 2014 I had analysed 40 BS readings taken with my meter (25% of these were fasting sugar levels) . The average of 40 readings during these 3 month eriod was 6.955 (i.e 7.0) . I had my HBA1C done on 22 September and that was 7.2% ( probably equivalent to 8.9) . I am at a loss, why HbA1C is so high where as my home readings for 3 months were much less .
Can anybody advise? My doctor increased my medication based on HbA1c reading ,though I though my own average readings were not too bad to get more medication .
I am wondering whether my meter readings were not accurate ? Or may be 25% fasting readings are not the representative samples to get the exact picture? May be the results at laboratory was somehow not correct? I really do not understand the correlation in between these two types of readings being so different.
Appreciate your views and comments.
 
Kaha said:
I am requesting the experienced forum members views on the subject above.
I am a T2 since 2005 on medication.
I had recorded blood sugar readings taken at home those were taken on a regular interval and at different times of the day . For the period from mid June 2014 to Mid September 2014 I had analysed 40 BS readings taken with my meter (25% of these were fasting sugar levels) . The average of 40 readings during these 3 month eriod was 6.955 (i.e 7.0) . I had my HBA1C done on 22 September and that was 7.2% ( probably equivalent to 8.9) . I am at a loss, why HbA1C is so high where as my home readings for 3 months were much less .
Can anybody advise? My doctor increased my medication based on HbA1c reading ,though I though my own average readings were not too bad to get more medication .
I am wondering whether my meter readings were not accurate ? Or may be 25% fasting readings are not the representative samples to get the exact picture? May be the results at laboratory was somehow not correct? I really do not understand the correlation in between these two types of readings being so different.
Appreciate your views and comments.
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The simple answer is that no matter how many finger prick tests we might do, we never really see the whole story. My meter readings are mainly in the 3s, 4s and a few 5s, yet my last 3 HbA1cs have been 5.3%, 5.1% and another 5.1% recently, so I obviously have higher periods I have not been capturing by my testing regime.

Although we think we know when we might spike, given our diets, I was astonished (and both slightly disturbed and comforted, in an obtuse way) to read someone on the Libre Freestyle thread stating that since he started using a more or less constant glucose meter (OK, it's not a CGM, per se, but close enough in this context) to see he had a significant spike from a curry (assuming it was the rice) at 5 hours postprandial. The spike was up to something like 9, if I recall correctly. And this guy is a T1 of many years standing who thought he pretty much understood his body and condition.

If your HbA1c is 7.2%, it probably means a bit more work, I'm afraid, if you want to pull it down, and potentially reduce your meds..
 
A similar thing happened to me on my last HbA1c test, which was 6.3% or 7.4mmol/l equivalent, but my own readings averaged 6.6mmol/l over the same period.

For one thing, our meters are not accurate. None of them. They are only required to be plus or minus 15% accurate.

If you are for example 5.5 first thing in the morning, then 7.5 at 2hrs after breakfast, then 5.5 again before lunch, unless you check every 10 minutes between breakfast and lunch you have no idea whether that 7.5 was your peak, nor how long you had been at those levels. Your peak may have been 10.5 at 1 hour, and your 7.5 may have been slow to fall, only falling to 5.5 a few minutes before you tested. Only the HbA1c test can tell you what your real average is. Our meters just show us trends.
 
You would need 8 or 10 tests a day for any comparison to an A1c result.
Simple reason 1 finger poke is just a snap shot of that moment in time. There is as you know 24 hours in a day so you need to be able to cover quite a bit of the 24 hours to see what is happening. An A1c is an average of about 3 months.
 
CarbsRok is right. While meter variations will average out with enough readings, unless you test throughout the 24 hr day, at evenly spaced intervals, independent of meals and insulin, you will never get anything approaching your real average BG.

Just think about meals. Most people would test before a meal and maybe 2 or 4 hours later. But what happens between those times? Those are likely to be the highest BG levels of the day. And they are being systematically ignored by the standard testing regime.

As a general rule, whenever Hba1c disagrees with a set of meter readings, it's the Hba1c that is right and the meter readings that are, not so much wrong, as just misrepresentative of the true average.
 
Thanks all for very sensible comments on the issue. After reading your comments, I do not think that T2 diabetic patients not taking insulin have much benefit from testing their sugar levels so frequently . Because such readings do not tell us much about the actual status of BS levels. Having said that now I understand why some doctors do not recommend T2 patients checking blood sugar levels and trust on A1c only. Now, is there still any argument why should we test sugar levels with our own meters?
 
One more question , how HbA!c can read accurate sugar levels for the 3 months? Can anybody explain it from medical points of views in simple terms without referring to too much technical details? I want to know ,because I got the impression that I need to trust on HbA1c only to know my actual status of sugar levels.
 
Put simply:

Blood glucose tends to bind itself to the surface of Red Blood Corpuscles (red due to the presence of oxygen-carrying compound, hemoglobin). The average lifespan of an RBC is 120 days ie 3 months. Therefore, measuring the number of red blood cells with glucose attached to them gives an idea of the blood glucose levels over the past 120 days.

The higher the levels of glucose in the blood, the greater the number of red blood cells with glucose attached.
 
Kaha said:
Thanks all for very sensible comments on the issue. After reading your comments, I do not think that T2 diabetic patients not taking insulin have much benefit from testing their sugar levels so frequently . Because such readings do not tell us much about the actual status of BS levels. Having said that now I understand why some doctors do not recommend T2 patients checking blood sugar levels and trust on A1c only. Now, is there still any argument why should we test sugar levels with our own meters?
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On the contrary, testing your blood sugar levels is very important for a T2. Just because day time meter readings don't predict hba1c very well, is no reason not to do them. That logic is the wrong way round. Hba1c tells you your typical blood glucose over 90 days. A meter tells you your blood glucose right now. The only way you can change the next 90 day average, is by changing the next 90 days worth of "right now" values. So no, you absolutely need to use your meter. Just don't place that much stock in it as an accurate predictor of hba1c.
 
@Spiker is right. A meter is an essential tool for type 2's trying to gain or keep control. We use them to test out different foods so we know what we can and can't eat. (and this changes as time progresses). Testing before a meal and after a meal tells us what that meal has done to our levels so we can amend the foods accordingly. Otherwise how would we know what, for example, a slice of bread has done to us?
 
I am always between 4.5 and 5.5 hardly ever go into 6 as per my meter but my a1c was 7.5 mmol, it was 46 but bluetit and pavlos helped me to convert it and it was that, I am a bit shocked too but I might have missed my peaks also I was travelling and had to eat a lot of pasta and white bread so I could put it down to that may be.
 
brettsza said:
I am always between 4.5 and 5.5 hardly ever go into 6 as per my meter but my a1c was 7.5 mmol, it was 46 but bluetit and pavlos helped me to convert it and it was that, I am a bit shocked too but I might have missed my peaks also I was travelling and had to eat a lot of pasta and white bread so I could put it down to that may be.
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Given what those of us with T1 have seen from continuous monitoring with bread and pasta, I'd expect that you'd have significant spikes after eating them that wouldn't be picked up at the 2-3 hour post prandial checks. It's worth doing a test 30 mins and 1 hr after eating on a couple of occasions, just to see how foods affect your BG readings.
 
HbA1C and daily meter readings are both very important but serve very different purposes. The 3 month average is a decent indicator but taken to the extreme can be misleading. Say your HbA1C is 6 for example, this could include lots of readings of 3 and 9 which is bad, although avg is good.
The daily meter readings do only give a snap shot but at least you can act on the information. It will let you know how well you tolerate certain foods and exercise. So, both sets of readings have their merits but one should not take the place of the other. Daily testing is so important.
 
Good, in such case we need at least 5-10 checks everyday . This will require a lot of strips . However, I can not accept the big difference and inconsistency between the findings such as average of 40 readings I monitored were nowhere with A1c . I can see some other forum members who posted their comments above had the same results. Anyway, I fully agree with your comments that we can understand the effects of certain foods and activities on sugar levels by doing tests at home.
 
Think of your Hba1c as a weighted average, while your finger pricks are an arithmetic average. Basically, the finger prick average takes all the finger prick results and divides them by the number of tests.

What the Hba1C is measuring is effectively the number of cells with glucose attached versus the total number of cells, which is the percentage value. For the sake of argument, for each minute that your blood sugar is above 0mmol/l, glucose is attached to red cells. A normal, non-diabetic will have a range within which the percentage falls, which equates to ~3.8-6.6mmol/l. With every mmol/l you are above that number, proportionally more glucose is attached and every minute below, proportionally less.

As an example, if you tested 8 times a day, on waking, pre-prandial x3, 2hrs post prandial x3 and before bed, and all of those readings were in the range 5-7mmol/l, you'd see an average somewhere near 6. However, in the two hour period post eating, your blood sugar is likely to spike to 9 or 10 and stay there for up to an hour, so over the course of the day your weighted average would be higher because you have spent nearly 10% of your day at a higher blood sugar than your meter readings are accounting for.

The only way to account for this is to test post meals at shorter intervals, i.e. 15, 30, 45, 60, 75, 90, 105 and 120 mins, or get a continuous monitoring solution.

Edit: Normal range updated following pavlosn feedback.
 
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Thanks , Tim for explanation .
But, as you suggested to test every 15,30,..........120 minutes after each meal is impractical. People will have nothing to do but test only the whole day .
 
Kaha said:
Thanks , Tim for explanation .
But, as you suggested to test every 15,30,..........120 minutes after each meal is impractical. People will have nothing to do but test only the whole day .
Click to expand...

You have missed the point. Meters for type 2's are not intended to be for anticipating our next HbA1c results. They are not designed to do this. They are for testing out foods and what we eat in order that we can find a diet that not only keeps our BS under control, but is also sustainable in the long term.
 
tim2000s said:
Think of your Hba1c as a weighted average, while your finger pricks are an arithmetic average. Basically, the finger prick average takes all the finger prick results and divides them by the number of tests.

What the Hba1C is measuring is effectively the number of cells with glucose attached versus the total number of cells, which is the percentage value. For the sake of argument, for each minute that your blood sugar is above 0mmol/l, glucose is attached to red cells. A normal, non-diabetic will have a range within which the percentage falls, which equates to ~4-5mmol/l. With every mmol/l you are above that number, proportionally more glucose is attached and every minute below, proportionally less.

As an example, if you tested 8 times a day, on waking, pre-prandial x3, 2hrs post prandial x3 and before bed, and all of those readings were in the range 5-7mmol/l, you'd see an average somewhere near 6. However, in the two hour period post eating, your blood sugar is likely to spike to 9 or 10 and stay there for up to an hour, so over the course of the day your weighted average would be higher because you have spent nearly 10% of your day at a higher blood sugar than your meter readings are accounting for.

The only way to account for this is to test post meals at shorter intervals, i.e. 15, 30, 45, 60, 75, 90, 105 and 120 mins, or get a continuous monitoring solution.
Click to expand...

A normal non-diabetic person would have an Hba1c of 4-5,9% (20-40mmol/mol).

The maximum non diabetic hba1c of 5,9% corresponds to an average daily glucose level of 6,8mmol/l, which is considerably higher than the 4-5mmol/l stated by you.

This does not of course invalidate the rest of your explanation, which is indeed excellent.

Pavlos
 
Kaha

I tend to think of the hba1c as my end of term school exam, while the self monitoring counts are the progress reports that provide the necessary feedback for me to take corrective action if needed.

Pavlos
 
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