Relationship between HbA1c and finger prick test numbers?

[pjgtech]

Still new to all this and still find this a bit confusing.
When I have my 3 monthly HbA1c blood test, the results come back with a number like 40 or 50 or whatever.
But when I do a finger prick BG test I get a much lower number, eg: 5 or 6 or whatever.
Now I know that the HbA1c test is looking at the blood sugars /glucose in my body over the last three months.
And the finger prick test gives an instant reading.
I get that with the HbA1c my GP/DN is looking for me to get to 40ish.
And I get that with the finger pricks BG tests my GP/DN wants me to get between say 4 and 8.
But why use different numbers and what is the relationship?
Why can't they use the same numbering system?

 

[Bruce Stephens]

Now I know that the HbA1c test is looking at the blood sugars /glucose in my body over the last three months.

Not quite. It's looking at something which is changed by glucose, glycated haemoglobin. Because red blood cells usually live for 2-3 months, HbA1c can give information about blood glucose over that time. But there's some variability, some of it understood (like anaemia and a genetic variation common in some populations) and some less so.

But why use different numbers and what is the relationship?
Why can't they use the same numbering system?

Because they're measuring different things. HbA1c is kind of giving an average blood glucose level over the last couple of months, but not really exactly that. So the units are different. There are certainly charts showing comparisons between average blood glucose and HbA1c (sometimes including HbA1c in the older percentage units too).

What is HbA1c?

HbA1c is your average blood glucose (sugar) levels for the last two to three months. If you have diabetes, an ideal HbA1c level is 48mmol/mol (6.5%) or below. If you're at risk of developing type 2 diabetes, your target HbA1c level should be below 42mmol/mol (6%).

www.diabetes.org.uk

 

[gail2]

Good advice hope it helps clear up the confusion

 

[Martin.A]

This is one of the charts that @Bruce Stephens mentions but you would need weeks of finger prick results (not random ones but fasting, pre-meal and 2-hours post-meal) to make any meaningful comparison with HbA1c, and even then it would only give you an idea of where you might be.

 

[pjgtech]

Thanks for the info. Ta...

 

[Burylancs]

Still new to all this and still find this a bit confusing.
When I have my 3 monthly HbA1c blood test, the results come back with a number like 40 or 50 or whatever.
But when I do a finger prick BG test I get a much lower number, eg: 5 or 6 or whatever.
Now I know that the HbA1c test is looking at the blood sugars /glucose in my body over the last three months.
And the finger prick test gives an instant reading.
I get that with the HbA1c my GP/DN is looking for me to get to 40ish.
And I get that with the finger pricks BG tests my GP/DN wants me to get between say 4 and 8.
But why use different numbers and what is the relationship?
Why can't they use the same numbering system?

They measure two different things. There is a complicated formula that tries to equate the two but it's generally not worth it. Upto about 2010 Britain measured HbA1cs in % like they still do in America. 6.5% (48 in new money) was the cut off point for dxing diabetes. The European Medical Agency decreed that HbA1cs should be measured in the new way and being good Europeans at the time we dutifully switched over. The measures ( 48 etc) were said to be a better scientific system and had the merit of separating the two things so that if somebody scored 6% they wouldn't confuse that as being an average of their own pinprick bg readings.
P.S. if the likes of Jenrick find out our current measures of HbA1c are a EU Directive, we might be going back to %. Heh, Heh. The EMA is a great European Institution, officiating on medical matters. It was based in London but Brexit meant we lost it and it went to Paris. And now the NHS is hanging on the coat tails of decisions made there without having a say in them.