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Re: [IP] Comparison of Lifescan One Touch Ultra to One Touch Profile
James Handsfield wrote:
>Meters aren't designed nor are they approved to be tested against each other.
Any two instruments can be tested against each other. It does not prove the
accuracy of either, which is extremely important for anyone doing it to
understand, but it can very effectively determine if the two machines
For instance, I can test two coffee machines against one another to tell
if, given the same grind, water, filters, and technique, they make
similar-tasting coffee. That does not mean that either coffee meets any
international standard. (If the coffee's brewed in the U.S., according to
the French, it qualifies as "jus de chaussettes" -- sock juice -- so it
certainly won't meet French standards. <g>) Both machines should simply
make similar-tasting juice, er, coffee. ;-)
As an end user, I am *not* trying to check the accuracy of my new meter
against a lab device. I am trying to verify that the sources of variation
present in design, production and in my home setting allow the meter to
behave as well as the one I already have. IMHO, this is a valid test.
Should the two meters perform differently, there are *many* possible
explanations. But I am not necessarily interested in identifying the source
of the variation. I am merely interested in finding a meter that correlates
well with the one I've got.
>The standard for accuracy and precision is set by CMS ... the readings
>[should] be within 5% of a laboratory standard (i.e. a moderate complexity
>test done in an approved lab) 50% of the time. That works out to
>approximately +/- 20%. With that much acceptable variability, comparisons
>between meters **cannot** statistically provide valid bases for comparison.
The tests that are done to qualify a meter may not integrate all sources of
variation. Production and user-introduced sources are of particular concern.
If one meter measured 200 mg/dl and another measured 120 mg/dl on the same
sample (a result I had in 1991), and similar discrepancies were found on
successive samples, one wouldn't need a lab test to conclude that there's a
problem present that would impact the use of the meters. One *would* need a
lab test to positively identify the meter that was more accurate. (In 1991,
I did go to the lab at my expense.)
>The only way for an individual to obtain anything near an acceptable test
>of their meter(s) (other than using the test control solution) is to do
>their own test at the same time as a tube is drawn for a lab test done by
>the method I mentioned above . . . and then compare the results.
This method would effectively measure the accuracy of the meter.
>And even then, if it's outside the 5% range, that's only one test. It
>must be done many more times before one will have sufficient data to make
>a legitimate comparison.
Agreed. Any claim about meter accuracy would need to adhere to such a protocol.
I didn't test meter accuracy, but I did compare two different meters. I
tested over 100 different samples. None was a calibrated standard, but I
was checking for wide disparities at any bg level. I never saw any.
Unfortunately for my bg control, I had the "good fortune" to test over a
wide bg range due to an incident with a dislodged catheter. ;-)
>Now if, for any reason, you suspect your meter is not as accurate or as
>precise as you think it should be, call the manufacturer. They generally
>have very liberal replacement policies.
IMHO, the best way I have of establishing a reasonable doubt about a new
meter is by cross-testing it with another one that's working "well". If
they're reasonably close (+/- 20%), the new meter's also working "well." If
they're much further apart (200 mg/dl vs. 120 mg/dl, say) and I have
confidence in my current meter's readings, I have no reason to make the
switch. Such "evidence" would not prove that the new meter was inaccurate,
but as a consumer, I have no motivation to accumulate such proof.
In 1991, when confronted with my doubts about the meter I was using, the
manufacturer was indeed helpful, but took no action with respect to the
strip lot I identified as tainted nor the testing and marketing of the
meter itself. I learned a valuable lesson from this -- the manufacturer is
NOT responsible for ensuring useful results in my household. The
manufacturer is responsible for providing equipment that meets appropriate
standards. OTOH, *I* am responsible for ensuring that the manufacturer's
equipment is fit for my use.
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