Question on the CGMS

I was wondering if anyone knew after your 3 days is up on your sensor for the CGMS do you have to disconnect the transmitter from the sensor and then act like it is a new sensor or can u leave the transmitter hooked up to the sensor and act like it is a new one. I am hoping you can leave it hooked up to each other cause i have like a a big piece of clear tape over it all and if i have to disconnect i am afraid i will pull the sensor out too. I hope someone can help me.



Jeff H

Hi Jeff.  I'm going to assume you are talking about the MM CGMS system.  You do NOT have to disengage the transmitter for the 2nd day period.  When the 1st 3 day period ends, just go in to your sensor menu and pick 'start new sensor'.  You'll very shortly get a prompt for 'enter BG now' and be set for another 6 hrs, then will have to do another calibration (just like the initial start up). You do NOT have to wait the 2 hr warm up period.  You do not need to remove the tape and transmitter until day 7,  at which time it will 'time out' and you'll probably start getting weak or lost signal messages.

A lot of people carefully remove the tape after day 6 or 7, being VERY careful to not disturb the sensor itself.  They remove the transmitter from the sensor (still embedded in your skin) and recharge it.  When recharging is done, reattach the sensor, tape it down and wait the 2 hours.  Some people are very successful in getting 9-12 days out of a sensor

Of might dislodge the sensor when removing the tape.  Or  you may opt to replace the sensor at day 7 if you have very good insurance coverage!  I sometimes opt to remove it after 6 days especially if the skin beneath the tape it itchy when i remove the tape.

Hope this helps!

Thanks for the help mcbaio. I could not remember what the educator told me to do. I called Medtronic minimed and they said that they could not tell me because the phone callls are recorded and they could be audited by the Government. And the FDA only approved them for using the sensor for only 3 days. So he could not tell me not a thing. He also said they are trying to get the FDA to pass for the sensor to last longer.  I wonder how DexCom's sensor last for 7 days. Meaning the material it is made of. I wish MM had one that would last that long or even longer.



Jeff H 

Hi Jeff.  The MM CGMS 'times out' after the 7 days,  but seems to get weaker signals after day 6.  It requires the restart at the end of day 3 and  day 6, but the transmitter does NOT need to be removed until 7 days have passed.  The newer European version of the MM pump, the Veo, is set up for I believe a 6 day initial timer, not the 3 day like the US version.  Hopefully the FDA will approve the newer Veo for US distribution.  Reposts from other pumper/CGMS lists indicate the Veo has a better algorithm for tracking.  Alas, we can only wait here in the US for MM improvements!

I understand the Medtronics lack of sharing details on the second start up after day 3......despite MOST users stretching their sensors as much as possible.  I've seen reports of people going a month or so on ONE sensor.  I myself have NEVER been that lucky.  I think 18 days has been  my upper limit for one sensor.  Usually I end of up pulling before day 12 due to erratic numbers or low ISIG numbers.

You might want to check out some other groups for more detailed info on the CGMS and which has both a pumpers and CGMS list.   There is also a group of CGMS users at , which can be subscribed to at this address .  I've learned a LOT of good tips through these groups and Juvenation!

Hope that helps. 


MM722 2 years, MM CGMS 1.5 yrs

Hi Jeff.  found some really great tips from other MM users and going to post them here!



From Liz:
With the Minimed system you will have to remove & recharge the transmitter after 7 days as it has a built-in timer.  Many people will use a sensor for only 6 days and some will restart it a third time to get that extra day.  Note that the time begins as soon as you attach the transmitter to the sensor, not when you do the first calibration. 

I try to get as much time as possible from each sensor so every 7 days I carefully peel off the old dressing to recharge the transmitter.  You do not want to pull the sensor out of your skin at all, so taping is very important.  Using tricks that I've learned here & on other forums and adapting them to my needs, this is what I do.

1. Insert a new sensor and place a strip of tape over the plastic hub, making sure the two little prongs that connect it to the transmitter are not covered.  Many people recommend using medical paper tape or similar but I find that a strip of Hypafix works best for me.  I have Hypafix rolls in various widths and a strip of the 2" wide is perfect.  Anything that will hold the sensor firmly in place will work.

2. I find that getting the dressing off of the transmitter is the hardest part.  Some people will place a piece of tissue on the transmitter or smear a little Vaseline on top to make the dressing easier to remove.  I have found the easiest way for me is to use some double sided *removable* Scotch tape.  When I connect the transmitter to the sensor I put some of the removable tape on top, then tape it all down.  Since both sides are sticky everything is held firmly in place but when I peel off the dressing a week later, it comes off easily.  The sides/edges of the transmitter are still stuck firmly to the dressing but once I get one edge loose it all comes up.

3. I keep a finger pressed on the sensor while removing everything because you do NOT want that to pull out of your skin even a little bit.  The strip of tape helps keep it in.

4. I use an alcohol wipe on my skin before inserting a sensor.  Let it dry thoroughly before inserting.  If I'm putting the sensor in an area where I know the transmitter has caused irritation in the past I'll slip a small square of gauze under the transmitter after it's connected and before I tape it down.  I make sure the gauze is not too thick because I don't want it pushing up on my transmitter.

5. When I remove the transmitter to recharge it I might clean the area up if it looks like it needs it.  The only problems I've experienced is irritation from the edges of the transmitter.  Using gauze or tissue underneath and avoiding areas that get irritated easily (my abdomen) solves that. 

6. The longest I've used a sensor was 34 days, and it was in my arm.  My arms do not get irritated by the transmitter and the site looked perfect when I finally took the sensor out.  It actually got pulled out by accident when I was trying to recharge the transmitter, otherwise I would have kept going since it was working perfectly.  That sensor tracked extremely well and was rarely off from my meter readings.  The site looked better than my infusion sets sites which are only in for 3 days.
From Wendy:
This post is to explain how to calibrate a CGM effectively to achieve 
overall good accuracy.
Also included is a description of the CGM's ISIG indicator and how to 
use it to guage confidence
factor for each calibration.

When you calibrate a CGM, you are telling it the current BG. The CGM 
compares the BG you enter
with the sensor's electrical output (known as the sensor's ISIG). 
Let's say that you enter a BG of 120,
and the sensor's ISIG at that moment is 12. The CGM then knows that 
the current ratio of BG to ISIG
is 120/12 = 10, so from that point forward, all future sensor ISIG 
values are multiplied by 10 to create
the on-screen SG (sensor glucose) display.

For example, if 10 minutes later the ISIG has increased from 12 to 13, 
the CGM's SG reading will
increase from 120 to 130.

Bad calibrations happen primarily for these reasons:
When there is an inaccurate BG reading (such as when fingers are 
contaminated with sugar)
When BG values are very high or very low. The sensor's ISIG at extreme 
BG values can not
be accurately extrapolated to the normal BG range.
When BG is changing rapidly. This causes the BG you enter to 
correspond to an ISIG that
is delayed in time.
Sensors near the end of life. Near the end of life, the sensor's 
sensitivity declines by the hour,
so the BG-to-ISIG ratio is not stable. A calibration with an end-of-
life sensor is good only for
a short time period, if at all.
Therefore, the following practices help to insure a good calibration:
Make sure hands are completely clean and dry before the BG. This is 
always important, and
especially important when relying on the data to calibrate your CGM.
Avoid using BG's under 70, or over 140 for cal's.
Only use a BG for a CGM cal if the CGM shows that BG has been 
relatively "flat" for the past half-hour
Never cal right after you eat. BG is already rising 15 minutes after 
you eat.
Never eat right after you cal. The CGM is counting on your BG 
remaining stable for 15 minutes.
(In other words, avoid eating both 15 minutes before and after you 
cal, if possible).
If you have no choice but to cal under poor conditions in order to 
keep the sensor from timing out,
be sure to do another BG test and cal as soon as BG stabilizes again.

The ISIG (short for Insterstitial Signal) is an electrical reading 
that is proportional to BG. In theory,
the ISIG is linearly propoortional, but in practice it is linearly 
proportional over a limited BG range,
which is why you always should cal when BG is within a normal range 
such as 70-140. Cal's at 50
or 300 might not linearly extrapolate into an accurate reading when BG 
is in the normal range.

The ISIG provides an additional tool to gauge confidence for each 
calibration. On the Minimed Guardian,
ISIG can be read by pressing the ESC button twice. Most other meters 
should have a similar option
to view the ISIG.

To make use of the ISIG to improve calibration confidence:
Each time you cal, look at the ISIG value at the time of the cal, and 
determine the ratio of BG/ISIG.
For example, you may find that a typical ratio is 15:1, or 8:1.
For the lifetime of your sensor, the BG/ISIG ratio will remain 
relatively consistent, but it will change
somewhat from cal to cal (which is why you have to do cals). However, 
if your sensor starts at a ratio
of 12:1, it usually will remain in that general vicinity during its 
useful life.
If you do a cal and find that the BG/ISIG ratio is substantially 
different from prior cals, it is an indication
that something might be wrong with the sensor. For example - Let's say 
you usually have a ratio of 12:1,
and then one cal has a ratio of 5:1. This is a suspicious cal. Check 
your sensor to see if it has loosened,
or if maybe it has been subject to physical pressure such as sleeping 
on it, or if it has been in use for it's
typical expected lifetime.
Another possibility when you see a suspicious BG/ISIG ratio is that BG 
just started to change rapidly
around the time that you did the test. Watch the CGM reading over the 
next 20 minutes. If you do see
a rapid change, cal again as soon as the BG stabilizes.
Finally, if you get a BG reading that differs dramatically from the 
CGM, don't jump to conclusion that the CGM
is wrong. It might be a contaminated BG reading. Always re-check the 
BG and don't re-cal the CGM until you
are certain the the BG is correct, or you may turn a good cal into a 
bad one.

There is always a possibility that the CGM will be wrong and you'll 
have a low or high bad enough to be symptomatic.
Not nearly as often though as relying on BG checks alone. The key is 
to follow good calibration procedure, and
to use your judgement at all times in interpreting the CGM data.

The incidence of false CGM readings can be greatly reduced using the 
methods above.

Here's an additional resource with even more complete