Please explain low ISIG values on the MM CGMS:)

I just inserted a new sensor and it will not work…keeps alarming (Lost Sensor, Bad Sensor) and the ISIG values are below 5! I started on the sensor w/o training and can find no details about interpreting ISIG values…mine have been low (less than 15 most of the time) w/ the previous 3 sensors yet they managed to work and track most of the time. I have done everything…checked the transmitter (ok)…although I wonder if it is tip, top. It is over a year old although sat in the box most of the time. Any help would be appreciated.

Thanks Mark:) I have had it in all day…since about 10:30 a.m. and it is now about 8pm. After dealing w/ it for a few hours, I turned it off and let it sit…then restarted and same issues. It just keeps alarming and when I enter data (stable) it gives me error messages. I think it must be a bad sensor.

Hi Patricia! The sensors do have expiration dates. Were the other ones that worked well expired? It may have something to do with it. There are varying opinions on sensor expiration dates though. MiniMed will of course tell you not to use them after they expire. I had the same thing happen to me a couple of weeks ago. I ended up taking it out. My ISIG’s will vary a lot and sometimes go to 5. I have found that if I have a 5 or lower for a long period my sensor usually will not read properly, alarm etc also. I have also been told that it is not unusual for ISIG values to vary. Good luck.

So long as teh ISIG is between 2 and 22 or 23, the pump and transmitter are communicating correctly. If the ISIG is blank, or if it is greater than 24 you have an issue, usually with the sensor. I have had good success calling MM if two sensros have failed in a row, and they walk you thru the transmitter test. On one occasion I had the transmitter fail, and had an ISIG over 200. On another occasion I had an ISIG over 50 and when MM walked me through using the test plug, it was determined it was the sensor.

rick phillips

Good thought…but, mine are from a non-expired box. My ISIG got down to 1.XX tonight, so I pulled it. Never got a reading out of this sensor…just kept alarming and wanting more blood sugar readings.

Thanks, Rick. Yes. I am going to call them and see if they will send out a replacement. I have never had numbers over 15 and I wondered when they dropped so low on this sensor. I did the transmitter test with the test plug and transmitter reads fine…ISIG 22 I think, if I remember correctly. It was odd because when I first attached the transmitter it did not flash, so first thing I checked was that transmitter was working and charged…checked out ok. I know one of the previous sensors I put in I had to monkey w/ for about 4 hours and then it started reading ok. I am scheduled to meet w/ the MM trainer next week…of course:) I was impatient and jumped in when I got the supplies. Probably something I am doing wrong! I follow the manual and watched the training videos on MM website…so, not certain what it could be. If you have some thoughts…let me know:) I think I am going to wait to place any more sensors.

Patricia, I sometimes get bad readings and errors as a result from not having a good sensor insert. Is there a MiniMed Rep. in your area that could give you some in person training? I had a 3 hour training with a Rep. when I started using the sensor…

Patricia I just typed in my responce to your question and had a computer shutdown and lost it all before I hit the add button so if you want to you can call me anytime and I can tell you all I know about CGMs and sensor and transmitters. You can reach my cell at 703-623-3884 I live in Northern Virginia just west of DC and will answer your call. I really do believe in the CGM system and want to help.

I had problems with bad calibration, and after the second one you have to replace the sensor. So, I was told by a rep. that if you divide your bg by the isig and it is anywhere from 1.5 and 20 it’s good to calibrate. That’s about all I know since I am also new to the cgm

Yes, I am scheduled for the “sensor and sensor start” class on the 21st:) w/ our local rep. Will be a first for me…usually go through my docs diabetes educator.

Thanks Anthony:) Just picked up this message…will wait to call you on a weekend if I am still in a quandary. I am hoping the class next week will clear much of this up. The real problems started w/ this last sensor…so, it may be that I just had a bad sensor or bad insert. I used my upper abdomen this time…not a lot of cushion there…wonder if I did not get it deep enough? or too deep? or if it hit some scar tissue? or something odd. I have been having these low (compared to what others describe) ISIG numbers…but, seems to still be working ok. On this last sensor, the ISIGs went all the way down to 1…which I thought was really odd. My BGs tend to run pretty low…so, was wondering if ISIGs reflect this? like amount of reagent being burned up by the glucose in the ISF? Also seems like different folks would have different amounts of blood sugar in their interstitial fluid (ISF)…because of differences in insulin receptivity. Basically measuring the glucose traveling to the cell from the capillary bed. Appreciate your insights and will be in touch should I continue to have problems. I am going to try to insert another sensor tomorrow a.m…took a break after pulling the other yesterday:)

Thanks Antonia:) I am pretty certain that my BGs were in that range…I remember being 80’s - 120 when I finally was able to calibrate. The sensor was reading bad from the start…meaning it was alarmed “Lost Sensor” right away. When it asked for me to enter a BG…it then started reading “Cal Error”, “Sensor Error”, etc. I am certain it read “Bad Sensor” after 2 BG’s were entered…but, it was a problem before that. I suspect, for whatever reason, it was a bad sensor or placement. I am going to try again tomorrow. Take care and thanks for your reply:)

Sometimes Patricia I will just “start sensor” with my existing sensor. Say I just put it in yesterday, but if I had the problems you were having, I would start all over. Hit “start sensor” and in maybe 5 minutes it asks for a calibration, and then see how it goes this time. Try it and see. I’ve had others do this and it worked, so who knows. I would try it before pulling the sensor. Ya got nothing to loose and maybe a sensor to gain.

Let us know how things go for you. Good luck to!!!

Well…that sensor never did work right and unfortunately, I had to pull it. Gave myself a day and then placed another…which also had somewhat of a bumpy start but, is doing ok today. I have better ISIG numbers (10-15ish) but, sensor can be up to 100 mg/dl off…sometimes higher, sometimes lower…so, not tracking very well. I am hoping it will settle down and read better tomorrow:) On the sensors that I have kept in, the 2nd day always reads better. I am getting pretty mellow about it…not watching it incessantly:) Look forward to meeting w/ the rep in a few days. Thanks for the recs Ron…yes, I have tried this as well and on the previous sensors it seemed to work. I really like the idea of CGMS and that it has caught lows in the middle of the night and allowed me to see trends in my basals that need work. I am for sure going to try the DEX to see how it compares…but, want to give MM the full benefit of the doubt. Will go through training and use up this box of sensors before making any decisions.

Well, this sensor is doing fine:) I restarted it on day 4 using the New Sensor trick and it was up and running just fine shortly after it asked for a BG. As experienced w/ the first 2 good sensors, the second day forward reads much better…I guess it gets calibrated and tracks better. I am hoping to get at least 6 days out of this one…my second sensor went 7 or 8 days. Today it is tracking w/in about 10 mg/dl which is MUCH better. I think these first generation sensors have their quirks…but, do look forward to getting some explanations when I meet w/ the rep…doing one of those sensor start classes w/ 3 other folks. Thanks to all of you who shared your insights and gave very helpful suggestions. Take care and will let you know if I learn anything of interest after meeting w/ the MM rep.

Good to hear. I will be anxious to hear what you learn from your rep. I am still having fantastic results with my MM722+CGMS. I always without fail get 6 solid day and have gone farther, but usually don’t mess with more. Six days is good for me.
Good luck.

I actually had a bad transmitter which I got with my setup in July.

I kept getting errors from the sensors over and over again as well as wild inaccuracy, and they replaced a bunch of them, but was having the same problems with the new batch, so they gave up and replaced the transmitter, and bang, works fine. (Still not always as accurate as I would like, but actually seems noticeably better than before, and I’m not having the sensor failures/errors.)

Just a follow up after going through the MM training…which was more like Q and A with a sensor start! Used one of the rep’s sensors…and it worked good at first. Had an ISIG of 98 which then dropped to 48 (was told this is normal start) but, then went to 0.0 w/in the hour…while walking around Borders! Did not get any greater clarification on ISIGs other than are a reflection of transmission strength and that high numbers are not unusual and they come down quickly to be anywhere from 5-20’s. Numbers below 5 suggest the end of life of a sensor or a bad sensor. I am beginning to think my problems are w/ the transmitter…so, I recharged it a little before putting it back on and changed out the battery in my pump (was down to 1 bar)…and between this and a little more time, the sensor seems to be working. So…a bit of a bumpy ride seems to be my normal. The trainer said my technique was good so, must be something else.

Trainer recommended anyone starting on CGMS print off and use the materials at MM website vs. the booklet provided (I had these along), never use IV Prep, don’t pinch up or hold site taut when placing sensors, place sensors at greater than 60 degree angle, and mentioned that many people lose sensors and require multiple placements to get one that works. At least I know it is not my sensors that are bad…may be the transmitter.

Have 2 more sensors in this box…then I am trying DEX. Hope I find something that works…really like idea of getting more BG info and protecting myself from hypos.

Thanks again to everyone who shared insights w/ me…I have learned a lot and appreciate my experience w/ the MM CGMS. I am sure I will find a system that works for me and know my control is better for it.