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Re: [IPk] Continuous Glucose Monitoring



Hi Terry,

I've been to several presentations about both the Guardian RT and other 
continuous monitoring systems currently being developed. One of the things 
that we *must* remember is that only earlobes, fingertips and toes provide 
us with convenient capillary blood glucose measurements. Subcutaneous 
sensors usually rely on interstitial fluid. In general you won't find the 
same amount of glucose in the capillary blood and the interstitial fluid at 
the same time. The margin of difference between the two readings is an 
indication of how close or far apart chronologically the measurements are. 
It takes time for blood to flow through all tissues of the body. Just 
because your fingerstick and your Guardian RT are not correlating at the 
time of measurement does not mean that the curves would not be 
superimposable though c.15 mins 'apart' if you did a venous or fingerstick 
bg every time the Guardian RT took a reading.

We have gotten so convinced that fingerstick bgs are the ultimate measure of 
accuracy but they're not. First, they are about 11 minutes 'off' from venous 
bgs; second, a fingerstick bg is +/-10% compared to a laboratory test. And 
it's the frequency of self/home bg monitoring that makes the numbers useful 
and helps us detect patterns and causes and effects, NOT their relationship 
to laboratory values per se.

The argument about whether continuous monitoring is accurate is getting 
almost as annoying to me as the argument over whether Shakespeare was 
anti-Semitic. Most continuous monitors (A) that have been developed do 
accurately measure interstitial fluid (B). Sadly, interstitial fluid (B) 
does not mirror capillary blood glucose (C). So: A yields B, but B does not 
yield C because A is not equal to C.


Melissa
Type 1 11+ years; MiniMed pumper 7.5 years; Animas pumper 1 year
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