What's in a number?

[Docb]

We have a lot of members, particularly those new to testing, asking about blood test results and what they mean or what is a "good" number. As many of you are aware I like numbers, mostly because they are what they are and do not have any opinion.

This morning, I woke up, got out of bed, did a finger prick and got a 4.3. Checked another finger and got a 4.2. Tried a third finger and got a 5.1. This led to me doing something I have wanted to do for a while and this was to take 10 consecutive tests on different fingers and both thumbs to see what the variation was. The next seven results were: 4.9,5.0,5.6,4.6,5.3,5.2,4.9.

These numbers leave me with a real conundrum. Do I panic over the 4.2 and start eating jelly babies to ward off a hypo or do I come on here crowing about the 5.2, a HOUSE SPECIAL or do I worry that the 5.6 is the start of a problem with high levels. Being me, I don't do any of those things, I put the numbers in a spreadsheet and do some calculations.

So I am happy to report that, this morning that my blood glucose was not 4.2 or 5.2 or 5.6, but that I do have a best estimate of my blood glucose which was 4.91+/- 0.88 (95% confidence interval). No jelly babies, no house special, no menu revisions, just another boring waking blood glucose of somewhere around 5.0 mmol/l.

What is the message from this? The main message for those who are new to testing is that you need to look at your numbers as a set, and base decisions on all the data, not just single readings. Even then, a difference of 2mmol/l from what you might expect could well be within the testing error. For old hands at testing, and all you T1's, yes I know, don't try and teach your grandmother to suck eggs.

I am not suggesting anybody does what I did as a matter of routine, I got the sore fingers so you do not have to. There is no doubt that blood glucose testing is a powerful tool when it comes to blood glucose management but like all tools it is important to understand its limitations.

 

[Toucan]

Many Thanks for this @Docb. - But your fingers must be feeling a bit tender!

It is very useful to bring some reality into the use of the finger prick results.
Even after 10 years or so of using my fingers as a pin cushion, I still tend to go into morning smugness or panic depending on what the meter reading is!

The most useful thing for me is the graph that I keep of morning readings and try to focus on the wider trend that it shows.
It is a very useful indicator of how things are going.

I have always found the meter very useful though on the '2 hours after eating something test' - as part of the detective exercise on finding out what my 'spike' foods are. i don't use it for this so much these days as I have the list of the danger ones, but still good for occasional use when I try a different food.

Many thanks for your finger sacrifice for the wider good!🙂

 

[everydayupsanddowns]

I do have a best estimate of my blood glucose which was 4.91+/- 0.88 (95% confidence interval).

Haha! that’s brilliant @Docb - really made me laugh out loud

But it’s an important point, and really worth making to anyone who is getting worried about the meanings of an apparent inexplicable ‘rise’.

We are very fortunate that most modern meters don’t often go anywhere near the +/-15% (ish) that they are allowed to 95% of the time, but it’s always worth mentioning that up to 5% of your fingerstick readings are allowed to be absolutely anything - even if you are completely scrupulous in your handwashing and sampling technique (and I know I am NOT!)

BG meters are an invaluable guide, but always recheck any result that doesn't match how you are feeling, and don’t sweat the small stuff and any occasional wobbles.

See also:

 

[Gwynn]

So, does that mean I can claim 5.2 every morning

 

[Docb]

@everydayupsanddowns, the variability comes from two sources. First is the accuracy of the meter and I suspect that is down to how consistent is the manufacturing process that makes the test strips. Second is sampling error, which I suspect is the more important as you suggest.

Either way up, the more important thing for me is that anybody who is thinking of buying a meter or has bought one and is starting out on the measuring rail should stop and think what it might be telling them up front. That way they can work out what they can get from it and stop worrying about what the small variations might or might not mean. That way you can defeat the argument that you don't need to test because it will only make you anxious.

And @Gwynn, yes you can providing your reading is less than 6.2 or greater than 4.2 (that's based on my data). Mind you I am sure that old pedant @Northerner would insist on you banging away with your finger pricker until you got an actual reading of 5.2 before he would accept it!

 

[trophywench]

Pedancy is not a solely male preserve.

Of course every one was different - they were not taken at precisely the same time.

😎

 

[Northerner]

old pedant @Northerner would insist on you banging away with your finger pricker until you got an actual reading of 5.2 before he would accept it!

No, that would not be acceptable, only the first number you see on waking is! Actually, the 5.2 was decided upon by member @KookyCat - originally the accepted 'lovely number' was 5.8 mmol/l, since this was the number used on all promotional material put out by the meter manufacturers 🙂 For example:



etc.