26 June 2018

Blood glucose meters. Are they so inaccurate that they're useless?

or, I have a blood glucose meter and I am afraid to use it.

Like many Type 2 diabetics, I have had my trusty blood glucose meter for several years. I have gone through phases where I have tested religiously several times a day, other periods where a struggled to test daily, and times when (I'll be honest) I have not tested for months.

Through all those times, I have assumed that my meter, a tiny and sexy Accu-check Performa Nano, had my back—that it was a trustworthy friend that dutifully put its best effort into measuring my blood glucose when asked, then told me the truth about what it found. Sure, it was temperamental sometimes, but what true friends aren't? Sure it would sometimes spit the dummy at a test strip or three, or generate unexpected errors with accompanying unknown numbers, but in an Italian car we call that "character".

But if Nano had a flaw, it was that I had to transfer all my test data from it manually. For this purpose I used Glucose Buddy on the iPhone, a full-featured and very useful tracking application, but I always hankered after a better way of doing things, that would allow me to track and monitor my results without having to key things in unnecessarily. Accu-check have PC software for this purpose, but in Australia they charge the quite outrageous price of around $130 for it, and according to the local diabetes association, are increasingly reluctant to part with the software to anyone other than health professionals—an odd stance in this information-centric and self-help world.

So I began to look at other options for meters that connected to PCs or iPhones. In the latter category there are very few players so far, and those that do exist are flawed for now. Lifescan, the makers of the OneTouch meters, had an iPhone app in the works but seem to have abandoned it. Glooko, a third party vendor, have software that will work with a number of meters, but required an expensive cable and sometimes a separate IR interface. The reviews I have read of it suggest that it's not yet a complete product. So the only real player is the iBGStar meter. It's problem is that it only connects to the old iPhone connector, so those with an iPhone 5 or above need to have a 30-pin to 8-pin adaptor, so the whole argument of portability and integration becomes weaker. A product that has been on the market a couple of years and hasn't kept up with the technology worries me a little. I know FDA approvals are slow, but surely if they were really committed to the product they would invest in a little R&D. Also, the iBGStar iPhone app seems a little basic at this stage. I'd like to track blood pressure and other information which it doesn't support. I've not ruled out this meter, but I am keeping a watching brief. [This paragraph is now a little out of date, and I'll be updating shortly]

Instead, I acquired a new OneTouch VerioIQ from LifeScan because it appeared to be an modern, attractive meter with a good range of features, and free software upon registration. It also came with a cash back offer greater than the purchase price, which meant trying one out would leave me in profit—a no-brainer, then.

Of course, being obsessive compulsive and having a new meter, I had to test, test, test against my old meter. And that's when the problem started. I'll get to the detail below, but the gist is not only do these two meters disagree with each other ALL the time, the also disagree with themselves MOST of the time as well.

And we're not talking small disagreements here. We're talking full on bloody feud, only the blood, alas, is mine!

Show me the numbers, I hear you ask, so here they are in the following table. If, in fact, I misheard you, and you really said something derogatory, then please feel free to skip to the next bit.


Evening 1

First finger
2nd finger

Morning post-fast

1st finger
2nd finger


2 hours after breakfast

2nd finger

2nd finger 2 minutes later

Before lunch

1st finger



not tested

Needless to say, I followed all the usual recommendations in my testing. Hands were clean, strips were kept in their vials until the last minute, they were brand new stock, and multiple readings were taken with the same blood within seconds of each other.

The first set of Verio readings and the last set of Nano readings were as I would expected. Tightly grouped and consistent. As for the others, they're a near random assortment. The last set of Verio results ranges from 4.9 to 6.9. The second set of Nano results from 7.4 to 8.9. When a machine can't agree with itself, it seems churlish to argue which might be the more accurate. However, that answer could only be decided with several lab tests as control, or with the use of a control solution. I will be acquiring some of that next week and will running more tests. I will probably also acquire another meter or two and go round again, all in the interests of science—watch this space.

Now the reason I am testing more frequently at the moment is that I have just gone on Metformin for the first time, and am gradually ramping up my dosage to find the correct level for me. And that requires me seeing a change in my readings in response to dosage (or waiting till my next 3-monthly A1C test—not the best way of assessing day-to-day progress). And if you are a T1 or T2 diabetic on an insulin pump connected to a meter, how useful is a meter this inaccurate? Worse still, the meters tend to be less accurate at their extremes, so there is danger of them failing to predict hypo and hyper events.

I'd be willing to bet that, as a long term diabetic, I could usually guess my blood sugar within +/- 20% based on time of day and what I'd eaten. In which case, how much is the meter really helping me?

Honestly, I am bemused, confused and more than a little angry. Fellow diabetes sufferers, we are being sold a lie by large pharmaceutical companies who care more about their own profits than our health. They rave about the accuracy of their meters, when standards only require +/-20%, i.e. a 40% range as compared to a venous lab test. So accuracy means no more than meeting this very loose standard, and even then many meters have been shown in lab tests not to even meet the standards.

I suspect that the meters from established manufacturers are all reasonably good in themselves—that given a decent consistent sample, they will return consistent, accurate results. The problem is, I am guessing, in the strips and the gathering and transmittal of the samples. The strips are fragile, unreliable and too affected by environmental conditions and handling. Manufacturer's proudly advertise "small sample size" and "fast response" as if these things were virtues, whereas it's more than likely that a slightly larger sample and a more careful assessment of it would yield more accurate results. At the expense of patient comfort, admittedly, but which one of us wouldn't sacrifice a bit of comfort if the results were much more accurate?

Let's raise our voices to both the manufacturers and the federal authorities that decide on the standards, and demand more accurate and more consistent BG meters. And let's encourage more independent testing of meter accuracy by centralised authorities with such data to be widely published.

Please share your views and experiences in the comments below. You may also like to read an article about meter accuracy and people's comments here.

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