Libre 2+ questions

[Amyfaith]

Hi all,

On my free trial of the Libre 2 plus, and okay, two days in, but you know me by now - I have *questions*! Hopefully these will be fairly straightforward.

1. So, the lag. Is this *predictive* of my BG right now, or just my actual BG 15 mins ago? I find things can shift about rather rapidly but momentary higher numbers on the home screen aren’t replicated at all on the daily graph, which suggests the former. I’m sure there’s statistical smoothing happening there but it doesn’t come even close.

2. I have zero body awareness and managed to run too close to a door today (inevitable). I have noticed some of the sticky bit is no longer fully stuck down. Is this going to cause a problem with water tightness when I shower?

3. I find BG reactive to movement on the sensor - like, I’ll be sitting and drop a full mmol/L within like 10 mins (and get up and go the other way). Is this just normal muscles-getting-glucose-to-operate stuff or something else?

4. I know accuracy isn’t fabulous, and as a tool it’s more useful for trends and early warnings, but is it considered normal to be out by fully 1 mmol/L fairly consistently? It is usefully consistent, so I just add 1 to whatever the Libre says, but is that too far out? I know things get funky at the highs and lows, but I would have expected fairly normal readings like I generally see (4-7) to be a tad closer.

TIA!

 

[harbottle]

1. I guess the s/ware using the readings at the 'current time' and before to predict where it's heading. This is why, when I have something high in carbs, I sometimes see a value of 8 or 9, but as it's working out what is really happening the graph drops.

2. Don't know.
3. Yes, I notice this. I can get up and move and it jolts up a bit then corrects itself. A shower causes mine to shoot up, but they eventually correct.
4. I find that the libre 2+ was quite close, but sometimes 1 higher than a finger prick. When the line has been flat for a while, they seem to generally be almost the same.

 

[Bruce Stephens]

1. So, the lag. Is this *predictive* of my BG right now, or just my actual BG 15 mins ago?

I'm not sure we have a good description of precisely what it's doing.

I find things can shift about rather rapidly but momentary higher numbers on the home screen aren’t replicated at all on the daily graph, which suggests the former. I’m sure there’s statistical smoothing happening there but it doesn’t come even close.

I think the graph is made just of the readings every 15 minutes. Those have been described: the sensor records one reading every 15 minutes, retaining all those for 8 hours (so if/when you scan, that can read up to the last 8 hours of readings). (It scans per-minute readings for the last (unknown) minutes too, but I think those are used for the arrow and the "current" reading and not the graph.)

3. I find BG reactive to movement on the sensor - like, I’ll be sitting and drop a full mmol/L within like 10 mins (and get up and go the other way). Is this just normal muscles-getting-glucose-to-operate stuff or something else?

I presume movement changes how the interstitial fluid moves, too, so I'd guess when we're moving that would make the interstitial fluid change a bit faster so reducing the gap between readings of that and blood glucose readings.

 

[helli]

4. I find that the libre 2+ was quite close, but sometimes 1 higher than a finger prick. When the line has been flat for a while, they seem to generally be almost the same.

The standard accuracy of all glucose meters, both CGMs and finger prick is only 15%. It is possible for your finger prick meter to be out, not just the Libre. As the accuracy is measured as a percentage, the absolute variation is likely to be greater, the higher your BG.
For example, if your true BG is 5.0, anything between 4.2 and 5.8 could be reported on either meter. If your true BG is 15, anything between 12.7 and 17.2 could be reported.
You may see a similar discrepancy between two finger prick meters.

The other thing to consider is that CGMs are less accurate in double figures.

Sorry, I am waffling. But basically, being out by 1 mmol/l is not significant considering the standard accuracy.

 

[harbottle]

If you google around you can find papers showing how these things work - linear regression and sampling and filtering data from the electrode... Interesting stuff!

I think the reason they are not as accurate when BG is falling/rising is because this changes the relationship between IF and glucose in the plasma. Sometimes it can change in the IF before it changes in the blood.

 

[Merluza]

If mine was out by only 1 mmol/L on a regular basis I would be very happy. I'm still being supplied the Libre 2. My current sensor is close when I take the 15 min time lag into account and often spot on so I'm content to rely on it as a general guide. My previous one was regularly 2+/- mmol/L low so I didn't rely on it at all. Both have been constant in their levels of accuracy or inaccuracy so I couldn't really fault them technically. Maybe the spot I choose makes a difference, my right arm seems to provide a closer, more stable reading but I may just be imagining it.

The jury is still out for me with the Libre 2. I've been using them for about 3 months now and can see the benefits but I was able to manage things just as well with finger pricks. I hope the 2+ is better.

 

[goodybags]

Hi all,

On my free trial of the Libre 2 plus, and okay, two days in, but you know me by now - I have *questions*! Hopefully these will be fairly straightforward.

1. So, the lag. Is this *predictive* of my BG right now, or just my actual BG 15 mins ago? I find things can shift about rather rapidly but momentary higher numbers on the home screen aren’t replicated at all on the daily graph, which suggests the former. I’m sure there’s statistical smoothing happening there but it doesn’t come even close.

2. I have zero body awareness and managed to run too close to a door today (inevitable). I have noticed some of the sticky bit is no longer fully stuck down. Is this going to cause a problem with water tightness when I shower?

3. I find BG reactive to movement on the sensor - like, I’ll be sitting and drop a full mmol/L within like 10 mins (and get up and go the other way). Is this just normal muscles-getting-glucose-to-operate stuff or something else?

4. I know accuracy isn’t fabulous, and as a tool it’s more useful for trends and early warnings, but is it considered normal to be out by fully 1 mmol/L fairly consistently? It is usefully consistent, so I just add 1 to whatever the Libre says, but is that too far out? I know things get funky at the highs and lows, but I would have expected fairly normal readings like I generally see (4-7) to be a tad closer.

TIA!

Evening @Amyfaith I recently trialed the Libra2Plus and I had a slight problem with it so I called the helpline and spoke to someone who was ever so helpful, apologised and sent me another so bear that in mind if you thought you were having any problems with the sensor.

also I was thundering, if you are prone to possibly in the future knocking into things (due to your zero body awareness) it might be worth getting some kind of cover

I bought some of the stick over patch covers (for when I go swimming) It you haven’t see them see my picture
they also come with a protective cap you put over the sensor before you stick the patch on, maybe look a look on amazon (or other online retailers)
I got these off amazon but there are loads of different ones available online if you wanted to try them.

 

[SB2015]

2. I have zero body awareness and managed to run too close to a door today (inevitable). I have noticed some of the sticky bit is no longer fully stuck down. Is this going to cause a problem with water tightness when I shower?

You could put another sort of tape over it to keep it in place for the two weeks. I cut a hole in the tegaderm I used when I did this to roughly match the hole in the centre to the Libre to let the sensor ‘breathe’.

I reckoned there was some sort of magnet in my Libre and the door frames around the house!!! My sensors have more tapes now so I no longer knock them off.

 

[Amyfaith]

Thanks everyone on this - super helpful. Sounds like I might need to drop Abbot a line just in case re: the door thwacking.

The accuracy thing is one of those things I’m going to have to keep reminding myself of - each meter/monitor will have its own quirks and ‘normal’. Like, as I think I said elsewhere, I’ve recently picked up a Contour Blue meter as the strips are significantly cheaper than the one I originally got. This meter measures, on average, 0.5 above my old one, which was a bit of a shock, I can tell you! (Even though I know individual fingers/strips can vary a lot, and have already seen some wild variations, I generally got very consistent and almost predictable results, so I sort of forgot that individual meters can be calibrated differently….) So really it’s a matter of reminding myself, constantly, of these being rough estimates. Weirdly this is easy enough to do when the Libre is telling me I’m in the low red overnight (Type 2s aren’t meant to have hypos, and if it’s measuring consistently lower than a finger prick, then it’s fine), but I find it harder to keep that in mind when I’m in my usual running area of 5-7 for no reason I can discern.

But thank you again, everyone. These are truly funky devices, though they seem slight overkill for me. I’ll definitely do another CGM run once the semester starts up to see how work and stress levels play into things, though (this one will finish up a week before we go back).