To Update BG on a pump: ISIG divided by BG

I am “upgrading” to an Enliite MM system. First tries sucked, so I went back to soft sensor and old pump. After 12 years on a pump, am going to training. My first experiences with enlite were horrible.

I called the help line and was told to never calibrate unless the result of a division of the current meter BG divided by the ISIG is 9 or less. A BG of 120 and an ISIG 8.42 is 14.25. When I extrapolate numbers, they are all way over 9–BG is 81, ISIG is 9 =9. That works…rarely.
Thoughts and experiences would be welcomed.

I don’t ever pay attention to my ISIG or do math around calibration like that. I usually calibrate first thing in the AM, or sometimes walk around in circles for 20 minutes, and then calibrate, when I get home from work or after my post-work workout, while I’m making dinner and then at bedtime. Most of the time, I will sort of babysit my BG to make sure it’s ok at calibration time. I’ve had pretty decent results with the Enlites but sometimes they seem to “fry out” when I have a big cardio weekend. I’ve sort of slacked off a lot lately but had a decent 10K run yesterday and 30 mile bike ride today, not huge but since then, I’ve calibrated my sensor (day 5…) a couple of times but it’s still reading 42 vs. 64 meter, so not too far off but not quite on the money. I just ate a couple of tacos and some black beans so I’m sure it will be flying up shortly.

The Enlite has a much higher Isig than a Soft Sensor. My currant Isig is 36 and my SG is 120 so that gives me a calibration factor of 3.3…

I have found over the last 14 days that the division factor is normally way over 9. I just calibrate. On the sofsensor it has been ok. The new Enlite… I will go to training, ask questions, and go from there. Very unsettling.

Officially the idea is that ISIG values between BG times 3-8.33 should be good. Having said that, I have gotten conflicting information over and over about that top value and when speaking with both the techs on the phone and local reps, there is major confusion over it being 8 or 8.33. In practice I would say that 8.33 is valid.

Having said that, lets think about MORE “rules” from MM on the subject of calibration.

Recently I was given the following information:

Only calibrate when BLOOD glucose (ie, meter reading) is within the following parameters:

20 for under 100 (all of these are BLOOD sugar numbers)

30 from 100 to 150

40 from 151 to 200

50 from 201 to 300

60 over 300

Why I wasn’t given this info at the start of Enlite training or why during the course of countless hours of tech support, is beyond me. I got Enlite in December. I just heard about this a week or so ago. Trying to calibrate when blood glucose is greater apart from sensor glucose supposedly will result in a CALIBRATION ERROR. Two of those in a row will generate a Change Sensor alert. Been there; done that…

Last night, around 2-3AM I checked my blood sugar and it was far different than my sensor (it’s been super accurate for 9 days) so knowing that ISIG’s will rise upon getting up for the day, I “cheated” by inputting a much lower number than my bg reading. When I got up in the morning my blood sugar reading was nearly identical to the sensor value. These sorts of “cheats” come from experience and i don’t recommend doing that until you know the consequences of varying the calibration number from the actual meter bg. AAMOF, I recommend keeping “cheating” to a minimum. I can go weeks and not “cheat”. good sensors require very few calibrations. Three per day seems about right from my experience and others that I’ve spoken with.

Medtronic’s CGM is finicky, there is no getting around that. How finicicky it is seems to vary from person to person. Some folks “just use it” and have great results. Others go through a learning curve of trial and error combined with Internet searches for helpful clues. Over time, they work it out and get good results with Enlite. I would put myself in that category.

Then there are the others who get so frustrated that they just walk away from it completely. Medtronic will have to do better than this eventually. But for now most can still get good results if they are willing to learn about what can go wrong when using Enlite and “don’t do that” as the old vaudeville joke goes. :blush:

Some comments about Enlite versus Sof-sensor (aka “the harpoon”). As was already mentioned, the ISIGs for Enlite should be noticeably higher than for the harpoon. Medtronic improved the sensor chemistry so that it performs better than the harpoon did. In my opinion, the Enlite ISIG when your BG is stable at 100 mg/dl should be from 20 to 30 … say around 25 +/- 5.

My guess at the moment is that for a properly working Enlite, the calibration factor which the pump calculates should be between 3.5 to 4.5. In my experience a calibration factor of 8 or more indicates my sensor has gone wonky on me.

While an ISIG of around 9 for a “normal” BG is perhaps reasonable for the harpoon (I actually don’t remember), with the Enlite I think I would suspect that something is wrong with the sensor. The sensor could just be defective. However, in my case an unexpectedly low ISIG usually indicates I’ve “kinked” or otherwise damaged the cannula.

####The inevitable Enlite tips" section

Some day I may get better organized and create an organized “tip sheet” for Enlite. But for now I’ll just point here, there, and everywhere with links to some suggested videos or documents.

But before doing that … Since you have had a lot of experience with the Sof-sensor, I wanted to mention that Medtronic now warns against using one common Sof-sensor “trick” with the Enlite.

Some Sof-sensor users claimed they got better results by inserting & then waiting overnight before connecting the Minilink transmitter to the sensor. Medtronic claims that letting an Enlite sensor “marinate” for hours this way can damage it. They recommend connecting the transmitter to the Enlite as soon as possible after inserting.

#####The Medtronic US training videos suck. Use the non-US ones
Medtronic Australasia has put together a collection of 7 YouTube videos called “Get Right With Enlite”. If you haven’t watched them, I recommend you do. They are still as boring as watching paint dry, but I feel they provide more useful information.

Here is a link to a post I made on another discussion site which lists the 7 “Get Right” videos and the links to view them on YouTube.

#####7 Tips from the ATTD Conference in a vlog from the UK

Below is a link to a YouTube video blog of Enlite tips from a fellow in England. These tips were apparently presented at an ATTD (Advanced Technologies & Treatments for Diabetes) conference he attended in February of this year.
Improve Enlite Accuracy: 7 Tips from ATTD Conference

#####A tips sheet (or sheets) from Gary Scheiner

I stumbled across the link below to a PDF document on the website of Integrated Diabetes Services, Gary Scheiner’s company. Tips for Success with the Medtronic 530G Enlite Sensor

I don’t know if I agree with or, in some cases, understand all of the tips. But it’s probably still worth a read.

1 Like

Phoenixbound: Thanks for the info. I am a bit dull on the parameters. Are you saying that if my BG from a fingerstick is under 100, I should only calibrate if the ISIG is 20?

John, those videos were very helpful. Much better than the Medtronic ones. Thank you for the information. This has a been a great help.

Nope, that’s not it at all. Those numbers (20, 30, 40, etc) are the DIFFERENCE limits between SG and BG numbers when it comes to calibrations. ie, if your BG is 100 and your SG is showing 50, you either have a bad sensor, your ISIGS have fallen because you have been laying down (and need time for the ISIG is rise from being up and about), or the sensor calibration is way off. MM is saying that you should delay calibration until the DIFFERENCE between BG and SG are within those tolerances. What I haven’t yet ascertained (but I will soon find out) is if they are saying calibrating outside of those requirements will throw out a CAL ERROR,or it’s just not recommended. I will report back when I get that info.

What I don’t like about that chart they gave me is that a one point difference in BG, say going from 100 to 99, causes the chart to claim one must then calibrate if the difference is less than 20 instead of less than 30. that’s obviously not the case in real practice as far as I can see, so I think its more of a generalization, rather than hard and fast rules.

Yes, of course. The help desk is trying to take what can be a rather complex analysis and boil it down to some “rules of thumb” to try to help avoid people feeling frustrated as much as they currently do … in my opinion.

As for calibrating when you’ve got a one point or even no difference, yes, I’ve done that. If it’s about 6 hours or more since my last calibration and my SG is not changing rapidly (no arrows), then I’ll probably go ahead and calibrate. It’s not going to really hurt anything in my experience.

I think the reason to avoid calibrating when your SG is in flux is because the Medtronic calibration algorithm averages the next three ISIGs and uses that plus your meter BG to derive the cal factor to use. If your SGs are changing rapidly, then that average SG is going to be less relevant.

Note: Actually it’s a bit more complicated than that since the previous calibrations also apparently are included in the derived cal factor if there are any. That is, whenever it is not the first calibration after either a Start New Sensor or Reconnect Old Sensor. I think that doing either of those will flush your previous calibration history.

I’m glad they might be of some help to you. But, to clarify, those are Medtronic videos. They just aren’t from Medtronic US. The “Get Right” Enlite videos are from Medtronic Australasia (ANZ).

The video blog from the fellow in the UK is not officially Medtronic, of course. But he says he works for Medtronic so … :wink:

My point being I am always surprised the Medtronic US seems to do so badly compared to their non-US branches. :angry:

AFAIK, “reconnect old sensor” doesn’t flush cal history but I need to confirm that. I’ll shoot a message to MM and get back on that as soon as I get a reply.

Here is the official scoop:

On Reconnect Old Sensor the last 4 calibrations ARE retained.

On Connect New Sensor, we are starting from scratch, waiting about 2 hours or so for first calibration…

If that’s the case then what is the difference between Reconnect Old Sensor and Find Lost Sensor. What does one do differently than the other?

I am going by unreliable memory here so I may be completely wrong, but I believe that when you do Reconnect Old Sensor the time until the next required calibration is 6 hours, not 12. In other words, the same procedure which is used for New Sensor.

On the other hand, after a Find Lost Sensor the required calibration time will be 12 hours because the previous calibrations are factored in.

So … I think whomever you contacted at Medtronic may be mistaken. But I’d have to try it again & keep notes to try to argue for this point in more depth.

Your turn to call Medtronic. :slight_smile: I wish they had fully informative training materials for us so that all of us users were given the SAME information and identical to the information that is accessible to tech support. I’d like clear explanations for:

  1. Reconnect Old Sensor
  2. Find Lost Sensor
  3. Why we disconnect for several hours and “reconnect Old Sensor” when ISIG’s are lower than they should be
  4. Why we remove the transmitter and “Reconnect Old Sensor” after 2-4 hours for when SG repeatedly doesn’t track with bg readings.

To me, shutting off the system for several hours, I was told, was to flush out recent calibrations, by virtue of time passage. To me, that negates my earlier comments about “reconnect Old sensor”, IF several hours have elapsed, does it not? ie, MM isn’t being very clear and this has been an ongoing issue of mine with their training. It’s all too murky.

ONCE AGAIN, A BIT CONFUSED… When I Reconnect lost sensor, or find lost sensor, I get beeped within minutes for a calibration. Am confused about the 6 or 12 hour wait times. Also, I have never lost a Cal with either of those functions.

I’m confused a little bit by what you wrote, but not all, as some things that have been posted on this thread aren’t accurate.

Normal Calibration requirements for ongoing sensors (forget the reconnect and lost stuff for a moment): 12 hour is a routine calibration requirement, and the 6 hour calibration (which you can do WAY before 6 hours if its convenient and bg is stable) is the SECOND calibration requirement following the INITIAL calibration ONLY for a NEW sensor (ie, you have installed a transmitter to a (purportedly) new sensor, and have chosen LINK TO NEW SENSOR).

Also, regarding an earlier post, think of the “chart” I showed with various bg variations (20, 30, 40)…to simplify, just think BG MUST BE WITHIN (roughly) 20% OF SG to get a good calibration (according to MM)

SO, if I reconnect the current sensor attached, I should get a 6-12 calibration requirement? OR wait for 6 to 12 hours to calibrate? Even a new sensor requires a calibration in a lot less time than that–2-3 hours.
With a Soft Sensor, I treat it like a new sensor after 3 days, restart, and it beeps me immediately for a calibration.

I am feeling really confused and unknowledgeable right now. What am I not understanding?

It works the same way with an Enlite. The number of days before you are prompted with a SENSOR END alert depends on the pump. If you have a 530G (or later) then you get a SENSOR END after 6 days (in the US). With the Paradigm Revel x23 pumps it happens after 3 days.

I am not completely sure when you do and when you do NOT have to go through the 2 hour WARM-UP process before calibrating a sensor. One thing that will definitely necessitate a WARM-UP is disconnecting and reconnecting the transmitter.

But, if I recall correctly, setting Sensor Off in the pump and waiting long enough before turning it on again will also prompt a WARM-UP. But I can’t remember how long is “long enough” and I certainly have not tried to do this recently to verify it. (It takes “too long” to test. :wink: :smirk: )

My best guess so far is that during the WARM-UP process the transmitter and sensor are getting in synch with each other. If you follow the ISIG level on your pump during each 5 minute interval of as WARM-UP it looks something like what’s in the table below.

<ISIG value> @ <time> every 5 minutes during 2 hour Medtronic sensor WARM-UP.
    ISIG 123.12 @ 13:34; 43.94 @ 13:39; 00.04 @ 13:44; 55.66 @ 13:49
    ISIG  00.00 @ 13:54; 00.00 @ 13:59; 02.14 @ 14:04; 25.02 @ 14:09
    ISIG  30.36 @ 14:14; 32.08 @ 14:19; 35.32 @ 14:24; 38.46 @ 14:29
    ISIG  40.38 @ 14:34; 42.18 @ 14:39; 43.26 @ 14:44; 45.40 @ 14:49
    ISIG  47.06 @ 14:54; 47.04 @ 14:59; 48.04 @ 15:04; 46.76 @ 15:09
    ISIG  45.78 @ 15:14; 46.74 @ 15:19; 47.92 @ 15:24;

Notice that initially the ISIG values are all over. But as time passes they get closer & closer to each other.

When you do not disconnect the transmitter, then I do not think there is a WARM-UP for any of the three possible “Link To Sensor” functions. You should just get the Meter BG NOW alert beep within 5 minutes because the sensor & transmitter are already “in synch” with each other from a previous WARM-UP.

1 Like