Howard Wolpert, M.D., on CGM in the Diabetes Clinic 9/14/2010

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dawheeler Posted: Mon, Oct 18 2010 11:12 AM

I believe Dr. Wolpert mistated  one of the advantages of the CGM as "With CGM, you have a probe in the skin that is continuously measuring the glucose levels. People get a readout on their receiver unit that tells them not only what their glucose level is...."

My Minimed Paradigm 723 does not provide real time glucose readings.  It is at least 20 - 30 minutes behind a finger stick check.  As Dr Wolpert said it is helpful for observing trends and glucose direction via alarms.  Do not use the screen graph for current BG levels.

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GreenGiant replied on Wed, Oct 27 2010 12:42 PM

You are correct that it is not really "continuous"  but it's pretty darn close.  The Minimed system actually takes a reading from the sensor once every 5 minutes.  That's 12 readings per hour, or 288 readings per day.  that is one heck of a lot more readings than people take using a meter with finger sticks alone.  The error in your post is that you say the CGM is 20 to 30 minutes behind your finger sticks.  This is not true.  There is no time relationship between your finger sticks and your CGM readings.  When the sensor is read once every five minutes those results are displayed virtually immediately, meaning in a worst case scenario the reading displayed on the pump display is 5 minutes old.  The thing you have to understand is that with your meter you are reading the level of glucose in your blood, which is fairly accurate with today's meters.  The CGM sensor is not reading blood glucose levels.  It is reading the glucose level of the interstitial fluid just below the skin's surface.  This is not as accurate as a finger stick blood glucose reading.  That is why the sensor requires periodic calibration using a finger stick as the reference.  When the reading on the display does not match the reading of a finger stick, which is most of the time, this is not due to the CGM being 20 or 30 minutes behind, what you are seeing is the difference in readings between the two devices, with the finger stick being the more accurate of the two.  If the pump shows a reading significantly different than a random finger stick it is time to re-calibrate the sensor, because it won' catch up by itself in 20 to 30 minutes.


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