ISIG levels

I’m not sure if my question applies to all CGMS users or if it is specific to Minimed.

I am on a trial with the Minimed CGMS. The trainer told me that the ISIG levels could range anywhere from 0 - 200, but that I should only be concerned if it goes below 7.

I’m on my 2nd day with the sensor and it has been pretty accurate. Yesterday my ISIG levels were 20-30 Today they are around 15.

Does this tell me something about the sensor accuracy or the expected duration? Does the ISIG continually decrease or can it also rise?

The ISIG number is the raw data number that the sensor extracts doing it’s thing. That number is then run through MM’s algorithm to get your sensor glucose number. Ideally, you want your BG divided by the ISIG to be between 1.5 and 20. That way you know that your are within acceptable range for a sensor calibration. Most of the time the ISIG number will increase with a rise in your BGs and decrease when your BGs fall. This is not always the case though. Confused yet? LOL The math involved in how they translate the ISIG into your sensor glucose reading is about 400 IQ points above my understanding but it works. When it comes to duration, the ISIG will drop sharply when the sensor is nearing end of life. You could go from an ISIG of say, 20 with a BG of 120 and then an hour later the ISIG could read 5 with the same BG fingerstick reading. You know at that point that the sensor is pretty much a gonner. Hope that helps a little.

Yes, this does help! Thanks!

And I also feel better about not understanding the ISIG, despite reading up on it. I can accept that my IQ is less than 400.

Do you have your blood sugars measured in mg or mmol? I think you’re in Hungary?
The isig correlates with your blood sugar level. I had several “bad sensor” alarms with the Minimed sensor. I was told it was okay to calibrate if the current blood sugar divided by the isig result was between 1.50-20.00. This has helped me keep the sensors working longer.

Someone when I first started on the CGM tried to explain it to me. Yeah, there was a whole lot of smile and nodding going on because I swear he was speaking some alien language! I had no clue what he was talking about. LOL

Good question Andrea. I’m an American living in Hungary … so I’ve been using mg/dl because that’s what I’m used to, but just this week, I decided it’s finally time to switch to mmol/L so that my doctors can read my logs without me spending hours to translate them. So my CGMS is reading in mmol/L.

So using my math skills, I guess that the rule translates to:

if my blood sugar in mmol/L divided by ISIG is between 0.083 and 1.11 then I can calibrate.

Right now it’s 0.39. So I guess it’s good!

Thanks for all the help!

The ISIG levels are constantly in flux as your BG rises and falls at various rates. I’ve been having ongoing calibration problems, so after several conversations with Minimed they gave me the following equation to sue when calibrating:

Test your BG. Divide your BG by the current ISIG. If that number is between 1.5 and 20.0, you’re OK to calibrate. I still get Cal Errors, but not as many.

What I believe is true too : when my ISIG off this moment is 15.06 …my BG is about half of this number…I tested at 6.4 !!. Active insulin .1 u, correction .2 u …so here goes.1 u normal bolus ( my pump is set for 5.5 )
To add to this : during the night , numbers were below low glucose level of 5 ( I changed this today to 4.6 ) and received a " few " warnings . My fasting number was 6.5 at 8.30 am , sensor showed 3.4 .Very questionable in my mind . I disconnected the transmitter and put it on the charger …this was day 21/2 of the second set of 3 days and I was NOT willing to discontinue YET …the area looks fine etc.
After charging completed , I continued as in " new sensor " and was happy I did , what I did .
It could be a case of having to change the battery ( sp ?) in the charger ?? I have only done this once and have this charger well over 2 years. Any suggestions/thoughts out there ?