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Precision Comes Before Accuracy

By David Mendosa

Last Update: November 11, 2004

The accuracy of blood glucose meters — or typically the lack thereof — has been a big concern of mine. I have written several articles about it. But first you have to know if your meter is precise.

Random acts of accuracy are worse than useless.

At least one of the meter manufacturers recognizes the importance of precision. Anyway, they call some of their meters that. You can buy the Precision Sof-Tact, the Precision Q.I.D, and the Precision Xtra from the MediSense division of Abbott Laboratories. But American manufacturers don’t sell any meters called “Accurate.”

A good definition of accuracy is the one that Consumer Reports used in its October 2001 evaluation of a few of the meters available then. Accuracy, the magazine says, is “how closely the readings agreed with standard lab results.”

Consistency, it says, is the “ability to give similar readings on successive tests of the same blood sample.” That's what I call precision. This is in line with The American Heritage Dictionary definition of precision as “The ability of a measurement to be consistently reproduced.”

Clearly, if you can’t consistently reproduce your blood glucose tests, your meter can’t possibly be correct, except once in a while. Random acts of accuracy are worse than useless.

Precision and accuracy are considerations with all devices. But they are particular concerns with our blood glucose meters where our health and treatment depend on them.

Fortunately, it is easy to test the precision of your meter, since you don’t need to compare it with anything else. It is a bit of a pain, however, because you need to run at least five measurements in a row on either the same blood specimen or separate specimens from the same fingerstick.

It is most useful to do this testing when you blood glucose level is in your normal range. If the overall variation in blood glucose from your highest reading to your lowest is greater than 5 percent of the average reading, you should view your meter with suspicion. You probably should not bother checking it for accuracy, which means comparing your results to those obtained by a clinical laboratory. And if the variation is more than 10 percent, you definitely need to get a new meter.

Dr. Richard K. Bernstein has been testing meters on himself and his patients starting in 1969 when he was the first person with diabetes to get his own blood glucose meter. “In my experience,” he tells me, “most of the meters that I have tested are unacceptable because of inadequate precision and need not be checked for accuracy.”

Sidebar:
What if Your Meter Fails Your Test?
If you blood glucose meter doesn’t pass your precision test, you need to try another of the more than 40 meters available in the United States. Check www.mendosa.com/meters.htm for the complete list.

I haven’t tested them all and I doubt if anyone has. But the meters with the best reputation for precision include the Ascensia Elite and the Ascensia Elite XL. Others worth considering are the Ascensia Contour, the Accu-Chek Advantage, and the FreeStyle Flash.

In addition, you might consider the Consumer Reports review of 11 meters that were on the market when they evaluated them in October 2001. Their top-rated meter was the One Touch Ultra, followed by the Accu-Chek Advantage and the original FreeStyle. 


This article originally appeared in Diabetes Health, November 2004, page 82.


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