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HBa1C and 90 day average

R

Roxanne

Active Member
Messages
44
Type of diabetes
Type 2
Treatment type
Tablets (oral)
Hi all, in two weeks time I have my first HBa1C (having been diagnosed in june).. I was wondering, will the result be similar to the 90 day average on my glucose tester or something completely different? My 90 day average is 6.3, that's not too bad right?!
 
Hi Roxanne
The HbA1c will probably be different from the average on your meter. It is an average of the last 8-12 weeks but the last few weeks count more than the weeks at the beginning of the period. Here is a link which will tell you all about it:

http://www.diabetes.co.uk/what-is-hba1c.html
 
If your 90 day BG average is 6.3 mmol/l then your HbA1c test results should hold no fear (you should be set for a HbA1c somewhere close to 6%, which is excellet).

Let us know how you get on!
 
I just want to point out that the A1c test measures a different blood factor than your meter measures. The numbers look similar, but they are not equivalent. Your meter measures the free glucose floating in your blood, and the A1c test measures the glucose clinging to your red blood cells. For example, an A1c of 6.0% is equivalent to an average blood sugar level of 7.0 mmol/L.
 

Sorry, but there's something majorly wrong with the site's converter. The correct formula converts 5.6 A1c to 6.6 mmols, although some charts seem to show 6.4. Note, the diabetes uk calculator shows 5.5 A1c converting to 5.4 mmol's! Think this should be looked at. Even if you change the calculation to allow for measuring whole blood rather than plasma it doesn't look right? And of course all our machines are referenced to plasma now.

One more thing Roxanne. The average shown on your meter is simply an average of all your readings. It isn't your overall true average for 90 days, as your meter doeasn't know what your readings are when you're NOT testing, and neither do we! So you can't convert your average reading straight to HbA1c. Nonetheless, your excellent results do suggest you'll have a good HbA1c result as well.
 

Grazer is right here - it only shows an average of your tests
 
This is the calculator on Jenny Ruhl's site, which is the one I use:

http://bloodsugar101.com/A1Ccalc.php

Jenny Ruhl is so current with the latest thinking that I am sure it is the most accurate available.
 
Caleb Murdock said:
This is the calculator on Jenny Ruhl's site, which is the one I use:

http://bloodsugar101.com/A1Ccalc.php

Jenny Ruhl is so current with the latest thinking that I am sure it is the most accurate available.
Click to expand...

Like all "calculators", they suffer from a bit of rounding. The standard formula most people accept is actually HbA1c=(AvgePlasmaBG+4.29)/1.98. The problem I mentioned in earlier post re- diabetes.uk calculator was that it used the formula for "Whole blood", (I think it's being changed on the site shortly). If you use whole blood, you have to multiply the outcome by 1.12 to arrive at HbA1c, hence the apparent difference. Nearly all meters today are referenced to Plasma.
 
Our calculator was giving out results for 'whole blood' blood glucose levels.

As is rightly pointed out above, most modern meters are giving 'blood plasma equivalent' numbers, which give a reading that is approximately 12% higher than whole blood readings.

We have corrected our calculator so that the numbers it gives will now be relevant to the vast majority of modern meters.

http://www.diabetes.co.uk/hba1c-to-blood-sugar-level-converter.html

As an example: an HbA1c of 6.5% gives an average blood glucose level of 8.6 mmol/L
 
Thanks Benedict - the whole blood / plasma confused me back in the past, particularly when US and UK meters were calibrated differently.

While on the topic of accuracy on the website, I was just looking at the A1C page:

http://www.diabetes.co.uk/what-is-hba1c.html

Where it says:

For non-diabetics, the usual reading is 3.5-5.5%. For people with diabetes, an HbA1c level of 6.5% is considered good control, although some people may prefer their numbers to be closer to that of non-diabetics.

I've just been told off in another thread for encouraging non-insulin (or other hypo-inducing drug) using T2s to try and keep their A1C down to non-diabetic levels, but I don't think I've ever seen a level as low as 3.5% ever referred to as normal.

Most authorities state somewhere like 4.6 - 6.0. Should this page be updated a bit as well, so as not to confuse people?

mark.
 
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