Thursday, May 11, 2017

Just a "standard" situation...

For some reason, even though we have a fairly strict rotation routine when it comes to Max's Levemir injection, we are now often confronted to frequent situations where the slow acting insulin seems to fail to act... I do not have a clear explanation for that: Max doesn't seem to skip his injection and there's no site/situation/meal/physical activity that I can correlate the rises with.

Anyway, here's such a situation, but also an illustration of many of the practical issues we face.

green segment: flattish around 100 mg/dl with a couple of mild compressions, no big deal.

By the way, a word about compressions: I often read very specific descriptions of compressions (transient sensor attenuations) in the T1D forums and groups. The compression should be abrupt, deep, and should end with a rebound. That is partly true: a major compression may indeed so unfold. But in practice, the compressions we detect and visually confirm can take almost any form. They can be partial, lead to fairly minor atenuations with no rebounds. They can be masked, as it is almost the case here, by a simultaneous increase. Be open: observe and learn: you may encounter compression lows, but also compression steady states or even compression highs (where the compression attenuates the ongoing rise)

third compression: that one is a major PITA. While it is detected, it masks - in a plausible way the rise that is happening at that moment.

compression exit: the trend starts to appear. But we need a few packets to make sure it is not one of those post-compression rebounds we see now and then. Unfortunately, another mild compression confuses the situation even more (and at that point, the compression detection algorithm, lacking a clear trend, has given up).

correction: the trend is now clear. Since we have seen such situation get out of hand quickly, the time has come for a quick Libre and blood check (see below): the Libre reports 230 mg/dl. The Roche Accu-check reports 225 mg/dl. The Dexcom still lingers at 160 mg/dl, one arrow up.

effect: as expected, around 6 packets later, the correction effect shows up.

Here's what the BG Meter and the Libre showed. Disregard time differences: both the BGM and the Libre are still running on winter time and both have drifting clocks. The actual time is 01:20 for everything.

A couple of comments on the sensors and accuracy.
  • the dexcom is running the G4 share 505 algorithm. The sensor is 5 days old.
  • the dexcom has been calibrated with the Roche Accu-Check BGM used here.
  • the dexcom is on the right arm.

  • the Libre is on day 12 of its life cycle.
  • that particular Libre sensor has been eerily accurate through the session.
  • the Libre is on the left arm.

I could be tempted to blame the Dexcom and praise the Libre and, to be honest, to some extent, I do.


  • this is the ideal situation for the Libre "delay compensation" algorithm. None of the fancy factors where it goes a bit crazy are present.
  • the Libre hasn't been compressed.
  • this Libre sensor has been noticeably better than average (MARD of 5% vs Accu-Check over the whole period, but not enough data to be statistically significant). 
  • that Dexcom sensor has been underperforming a bit for reasons that I can't be certain of.

And what about the correction?

I hit hard. Very hard. Based on our experience, when the Levemir injection seems to fail, EGP can spiral out of control (we did get our first even 400 mg/dl on such an occasion). I used about 2.5 times more insulin that I would use to correct that trend in daytime.

There's always a bit of anxiety when using such a relatively high dose (8U) in the middle of the night. I do want to avoid the yo-yo situation where I have to correct a low later. And, at first, the huge drop after the plateau isn't reassuring. What is the fall accelerates? That is always a question that lingers.

As it turns out "insulin resistance", or EGP, or a mix of both is so high in those circumstances that the situation should evolve well. But that is an opinion based on our fuzzy experience and gut feeling, not a computable one, if only because the previous nights were OK and we have no definite idea about the current insulin sensitivity level.

As you can see, the trend settles quickly.

And even if I am usually very confident with my decisions, I will lose a few hours of sleep, keeping an eye on the situation just in case... and write this blog post to kill time.


  1. T1D since about 4 years, using Lantus (~24h working period). In the first 3 years, I don't think I've had Lantus go bad on me (and I used to use a throwaway pen for much longer since I needed less). In the past few months, I've had plenty of situations where I get:

    1. BG that always seems to have an incline (upwards)
    2. Need to use quite a bit more short-term insulin (Humalog) over the day.
    3. BG much more spiky, and just higher in general (avg).
    4. When I switch to another pen that I've been keeping in the fridge, BGs stabilize after ~2 nights.

    None of this is measured scientifically, it's a feeling I'm getting. Maybe it's me, maybe it's bad injection sites (though I don't change sites when I change pens). I should probably write it down more. Correlation, causation, I don't know. Just wanted to add an unreliable data point. The first paragraph of your blog triggered me to write about it.

    (I use a Libre with the Glimp app (raw values) to measure, and spot check from time to time)

    Thanks for your writing by the way, it's very interesting and one of the only two blogs about diabetes I read (along with I started reading with the Libre reverse engineering and I haven't stopped since.

  2. Thanks for your kind words about the blog. Hope you got my private response.

  3. Seconding the comment about the blog, very informative!

    Regarding these situations with your son: have you ever suspected pollen allergies? This is what causes very unpredictable basal insulin performance at least in my personal case. Very annoying as not foreseeable, and there and gone from one day to the other with an otherwise pretty manageable T1D.


  4. Thanks Markus. Interesting suggestion indeed. While my son has no demonstrated pollen allergies, he has had more of some fuzzy respiratory issues (to the point we considered dust mite allergies, changed his mattress and treated the bed). On that aspect only, it seems (I think it was on the FDA approval data that I saw this, not 100% sure) there was also a significant increase in upper respiratory tract infections with Levemir. Add that to the typical carelessness in handling insulin, storing or even closing pens, and unreliable self reporting typical, possible site issues... in a teen and you end up with a pretty confused global picture...

  5. Hi Pierre, thanks for attempting to send me a response! I'd very much like to read it, but I don't see it in my mailbox. It's "alonzalazar"+"@"+"" (don't know how well blogspot does native email obfuscation, so excuse the mangling). I hope it works :). Thanks again.