Blood glucose numbers - what do they mean?

[Peter 9611]

Can someone explain the numbers system to measure blood sugar levels please?

 

[Leadinglights]

Can someone explain the numbers system to measure blood sugar levels please?

Welcome to the forum
There are 2 ways in which blood glucose is measured and they have different units so when quoting numbers it is always necessary to give the units.
In the UK
An HbA1C test which is used for diagnosis and is done from a blood sample taken from the arm and sent to the lab is an average of your blood glucose over the previous 3 months in basic terms. The result is in mmol/mol (used to be given as a %) The diagnostic threshold is anything over 47mmol/mol is diabetic, 42-47mmol/mol is in the 'at risk' or prediabetic and below 42mmol/mol normal.
Readings done from a blood sample from a finger prick and measured on a small hand held monitor is a blood glucose level at that moment in time and is given in mmol/l.

 

[Docb]

Hi @Peter 9611 and welcome to the forum. Just to add to @Leadinglights post.

Newbies are very often confused by the tests and the numbers produced. There are two types of measurement.....

1. HbA1C. This is the test used for diagnostic purposes but does not measure blood glucose directly. It is a laboratory test done on a sample of blood taken from a vein. If you want to know what it actually measures then google it and get the details. The upshot is the result can be used to take a view on your overall blood glucose control. HbA1c changes slowly and so can be taken at any time with no advanced preparation. The result is usually given in mmol/mol although sometimes it is expressed as a percentage. The interpretation is as above.
2. Blood glucose measurements. These directly measure the amount of glucose in your blood and is expressed in mmol/l. It is what you get from a hand held meter. Unlike the HbA1C it varies quite a lot in the short term, mostly depending on what you have eaten and how long before the test you ate it. As such, interpretation of the results is not straightforward. It is an excellent test if you are experimenting with diet and want rapid feedback to allow you to make adjustments. T1 diabetics can use them to adjust insulin doses and to cross check readings from continuous monitors.

So both tests tell you something about your diabetes and the picture above gives you an idea about how they are related. The blood glucose scale sort of represents the average blood glucose you might get at any given HbA1c.

We often, on the forum, get questions asked about converting the results of spot tests to an HbA1c result. There are ways of going about that but it requires a lot of analysis and for me is one for the nerds. What you can say is that if your Hba1c measurement is high, then this will be reflected in the range you get with spot readings.

So, as a rough rule of thumb, an HbA1c of 48 mmol/mol will result in an average of spot readings of around 8 mmol/l with individual readings ranging from lows around 5 mmol/l to highs around 10 mmol/l.

Hope that helps a bit. Don't worry if it doesn't, you will get the hang of it as time progresses!

 

[Proud to be erratic]

This question seems to bubble up quite frequently. Could I suggest; @Docb, that you consider slightly altering the title to "Blood Glucose Numbers", add a tiny bit more about %s that sometimes are used instead of HbA1c (and how to convert those) then pin this thread near the top of the Newbies section? Just a thought.

 

[Docb]

This question seems to bubble up quite frequently. Could I suggest; @Docb, that you consider slightly altering the title to "Blood Glucose Numbers", add a tiny bit more about %s that sometimes are used instead of HbA1c (and how to convert those) then pin this thread near the top of the Newbies section? Just a thought.

Good shout -- changes made 🙂

 

[everydayupsanddowns]

As others have said HbA1c results were previously given in % units (this is still used in the US I think).

The result is the same, it’s simply a different way of expressing it, either by % of the affected red blood cells, or their mass (or something!)

You can convert an HbA1c from mmol/mol to % (and back again) with a mathematical formula. Or there’s a handy converter on this page:

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

Along with other helpful information about the HbA1c check itself.

 

[everydayupsanddowns]

For those who are self-monitoring capillary blood glucose, the usual suggested ranges are:

Type 2
4-7mmol/L before meals and
No higher than 8.5mmol/L by 2 hours after meals

Type 1
5-7mmol/L before breakfast
4-7mmol/L before other meals and
No higher than 9.0mmol/L by 2 hours after meals

For those using sensors, the International consensus recommendations for Time in Range can be helpful in interpreting results over weeks and months.

 

[everydayupsanddowns]

This is also worth remembering if you get confusing results from fingerstick glucose meters.

BG meter accuracy
It can be quite disconcerting for members new to self monitoring of blood glucose to get different results from BG readings taken close together, even when carefully following manufacturers guidance (washing hands etc). All meters for sale in the UK should comply with the following ISO standards 95% of the time, which allows a degree of variation (and 5% of results can read anything at all). If in any doubt, or if a reading doesn’t match how you are feeling, you should check again with a fresh strip.

 

[everydayupsanddowns]

For those using sensors, who find that there are confusing differences between fingerstick capillary glucose readings (BG meter) and sensor glucose values, this list of precautions and limitations of sensor glucose might help explain things

CGM limitations and precautions

Moderator Note: This helpful reply was copied from another thread as it details some of the commonly experienced limitations of continuous glucose sensors. My blood sugar has been in perfect range for days now, but although I haven't changed anything, I'm starting to get very short periods of...

forum.diabetes.org.uk

 

[everydayupsanddowns]

Sorry for hijacking your thread with all this extra information @Peter 9611 - but it‘s such a good question, and handy to have all this information gathered in one place for other newbies!

 

[Anxious 63]

i have found my meter and sensor gives me a higher blood sugar than the blood finger. i it usually shows mine about 2 points more than the finger test , as anybody else experienced this

 

[everydayupsanddowns]

i have found my meter and sensor gives me a higher blood sugar than the blood finger. i it usually shows mine about 2 points more than the finger test , as anybody else experienced this

Differences between fingerprick capillary blood meters and continuous sensors are not uncommon @Anxious 63 and can happen for a number of reasons. Generally sensors are design to work within a modest degree of accuracy from lab results called MARD (mean absolute relative difference)

Of course, fingerprick meters themselves are not always 100% accurate or in line with lab results either - so effectively we are comparing 2 different systems, both with theie own margins for error.

They both provide helpful information in their own way though. If you feel that a sensor is not performing as you’d expect it to the best bet is to contact the manufacturer who can troubleshoot the sensor, and will most likely replace it if it’s not working as expected.

 

[Anxious 63]

Hi there everyday i had a feeling you would reply being one of top experts on here , yeah its strange in hospital the doctors and nurses said the blood finger is more accurate

 

[Docb]

@Anxious 63 - I am on a one man campaign to try and stop people thinking about the "accuracy" of one measuring system relative to another. Thats because you can only measure "accuracy" against a known standard. What you cannot do is compare one instrument with another and say anything about their accuracy. You might be able to say something about reproducibility and you can say something about the difference between instruments if you compare lots of readings taken simultaneously, but accuracy, no.

The real question is, can you use the numbers they give to make sensible decisions? My opinion is that despite what number it gives on the screen, all the systems are capable of providing just that. They will all tell you what ballpark you are in with regard BG, they will give you an indication of whether things are changing, and whether the number you are getting is roughly what your experience tells you that you ought to be getting. That will give you what you need to manage things.

To me, the real advantage of CGM is the convenience in the way the data is grabbed, basic data analysis done and the results displayed. It is also the gateway to closed loop systems that do adjustments for insulin users automatically. The downsides are the cost relative to finger pricking and all that tech can fall over if some third party decides to update something somewhere without making sure that it will still work.

PS...If anybody in a hospital told me that one was more "accurate" than the other, I would ask them to prove it!

 

[Anxious 63]

Yeah Docb you make some good points there .just a bit confusing if somebody was 13 as opposed to 16 it might make somebody like me panic , and then have some turapi and then have an hypo , ye cant win sometimes

 

[Proud to be erratic]

Yeah Docb you make some good points there .just a bit confusing if somebody was 13 as opposed to 16 it might make somebody like me panic , and then have some turapi and then have an hypo , ye cant win sometimes

Well both 13 and 16 are telling you that your ballpark figure is high and many of us might want to take some steps to reduce. For me whichever device is the lesser wouldn't matter, I personally would be considering correcting from 13 regardless.

However both Dexcom and Abbott say if their CGMs are out of range (4 to 10) then trust the FP in preference to CGM.

But more importantly what are the trend arrows telling me? If both have been pretty well static at each of 13 and 16 respectively then I might take an average. If there is a lot of BG change going on anyway I'd go to my first reaction, correct back to 13. Or BETTER just wait 20 mins and see if that all settles to no change andvhorizontal trend arrows. Neither level is seriously a problem for 20-30 mins.

 

[Anxious 63]

thanks for that advice proud will do that thanks mate

 

[harbottle]

i have found my meter and sensor gives me a higher blood sugar than the blood finger. i it usually shows mine about 2 points more than the finger test , as anybody else experienced this

Yes, I find that libre sensors are quite a lot higher than finger pricks. I've had sensors showing 8 when a finger prick was showing 5. However, I also found that during their lifetime the sensor results become less consistent (Usually after around 10 days the readings shoot up even higher - probably fouling of the bit that's inserted into the skin.)

Still, they are impressive devices and I know a T1 who finds them absolutely indispensable.

There are so many factors that can affect readings in finger prick readers - temperature, contamination, quality of the components, the software, the enzyme, etc.

 

[trophywench]

Since my pump ONLY communicates with its matching BG meter and the insulin dosage (aka the Bolus Wizard) is calculated by the meter not the pump itself, whatever my Libre happens to read at that exact moment, I cannot possibly rely on the Libre for practically anything except trends. When I do, it has to be intelligent guesswork and mental arithmetic, both of which are OK but come on - I've been doing this for over 50 years by now so what happens when my brain isn't functioning 100% - which some days I'm pretty sure it doesn't. One of the reasons I'd be/will be stuffed if/when anything happens to my husband cos I haven't driven for years now - and he's actually nearly 2 years older than me and got different health worries himself.

 

[Hak92]

For those who are self-monitoring capillary blood glucose, the usual suggested ranges are:

Type 2
4-7mmol/L before meals and
No higher than 8.5mmol/L by 2 hours after meals

Type 1
5-7mmol/L before breakfast
4-7mmol/L before other meals and
No higher than 9.0mmol/L by 2 hours after meals

For those using sensors, the International consensus recommendations for Time in Range can be helpful in interpreting results over weeks and months.

Thanks for this info, if I was to spike up to 15mmol/L within the 2 hour window after eating but came back down to below 9.0mmol/L within the time frame would this be okay?