Cheerio spikes on FreeStyle Libre, but not on BG monitor

Hi,
My son is 6 years old, diagnosed recently type 1. We have been using the FS Libre for 3 months now. We had problems with the system recently, so we've been comparing the Libre readings with his Accu-chek Aviva Expert monitor readings over the weekend. He's on 7 units Lantus in the morning (better control than giving at night) and between 1:20 & 1:15 ratio novorapid at least in the morning
This morning, he had Cheerios for breakfast. It's high GI so we give 1.5 units about 10 minutes before and another unit when it starts spiking. On the Libre the last few weeks that process has seen it go up to about 10 then come down nice and smoothly to the 5's throughout the morning. No blood pricks needed at all.
Today, About 45 minutes after eating breakfast, his libre said 12 and an arrow going up. We did a blood check which showed 8!! Libre 10 minutes later (my wife teaches at the same school so she did a check in the playground before the class went in) showed 13 still going straight up. We thought the Libre would show the levels coming down nearer to 8 within about 15 minutes.

My question is, why the huge difference between sensor and monitor? Is it the high GI? Does it affect BG and interstitial wotsits differently? The numbers for everything else were so similar last night and early this morning, within a 0.3 mmol/l of each other.

I would greatly appreciate any input on this, Thank you all.

kitedoc said:

error rate of sensor and glucose meter

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Can you explain that please? In the night and first thing in the morning, they were 4.3 & 4.5, and 5.6 & 5.5 respectively.

kitedoc said:

May depend on the error rate of sensor and glucose meter.
Why give him Cheerios if it spikes his BSLs??

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Because he's 6 years old and wants Cheerios. We have insulin

kitedoc said:

That is one way to do it but ... Are we just continuing to be duped by the cereal companies which have been duping us all ever since Dr Kellogg made cornflakes over a century ago ??

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Thank you. That doesn't help my question. But it reminds what a South African doctor told me once about cornflakes. "ehts jist laak eading pinsil shayvings"

kitedoc said:

Each brand of meter has an error rating. That is when tested against a god standard like a lab blood test it may be out by +/- x %.
Glucose meters these days are supposed to have an error rating less than +/- 15 % but also depending on the BSL that error rating may be worse or better at say lower or upper ranges of BSL.
I have read that the Contour next meter has a +/- 5 % error rate which is said to be best in class. And I use my Contour Next meter as the one I believe over anything else at home.
I use a different meter when out and about because it is smaller, more compact and it also reads ketones on a separate strip. I will use it if needed to read ketones at home as well but its error rating for BSL is nearer +/- 12 %.
The same applies to the Libre. It has an error rating but I am unaware of the figures.
I do know some find that the Libre reads too low at times. If you type 'Libre' into the search box upper right corner of the Forum screen you can find past threads (topics and posts) about it. Most people I gather use it for trends rather than accurate BSLs readings..

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Thank you very much.
We do use the freestyle for blood checks as well, but find them too to be out by 1-1.5 like the accu-chek monitor. However, the first two months we did not notice such big differences, and they are mostly within 0.5 of each other.

Knikki said:

Hello @Joesdad

There is nothing wrong with eating cereals if that's what you do.

However.

The problem with all cereals is that they are high in carbs, which can take a while to be digested and get absorbed by the body.

This is where the "spike" comes in. Take me for example, I will eat a mix of at least 3-4 cereals which can be a fair amount of carbs. Now if I inject to cover this odds on my blood stars will drop, but I know that 3-4 hours later my bloods will go way up, hence "spike"

As for the Libre, well that could be down to dodgy sensor as I have had it before now where Libre has said 16.5 yet bloods say 10.4, it's just one of those things. If the sensor continues to be out, by as much as you say, then I would contact Abotts and report it, they may replace it free.

The other thing, rereading your post, when did you attach the sensor?

Many of us find that when you first attach them then activate it, the first 24 hours can give "interesting" readings.

What many of us do is when the sensor is due to be replaced, we stick a new sensor on BUT do not activate it, basically let it sit there for anything upto 24hours, which can give better more consistant readings.

Can't help on the GI foods as I gave up using that index years ago.

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Hi @Knikki ,

Thanks for your reply.
Firstly, we find the problem more with Cheerios and coco pops etc, i.e. sugary cereal than with Bran flakes and shreddies. Obviously both are hi-carb, but the sugary ones send it soaring much quicker. The question is why was the blood reading much lower?

Regarding the Libre, we have had dodgy ones, and in fact just had 3 replaced, (you can see my first two ever posts for details on that saga). This one has settled down now, and we'll try again tomorrow. But it won't shock me if the results are similar.

I like the idea of attaching 24 hours before activating, so we'll see to it in 13 days time.

smc4761 said:

I have also found that the Libre is fairly accurate when BG are between 4 and 12. Anything above or below these figures they can be out as much as 20%. I am sure that you aware that Libre in measuring interstatial fluid, whereas the Accu chek will be measuring blood

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Yes, that was a surprise when I discovered that. The fact that they are measuring two different things, makes me wonder whether BG reacts differently to sugar, to how interstatial fluid reacts. But, it is no longer such a mystery that the readings are soooo different to each other.

Knikki said:

Roughly that kind of time line sometimes 5 hours.

Why?

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Same here. The insulin lasts 4 hours, but the carbs can only hit sometimes after 5. Try Wholemeal bread toast with full fat cream cheese topping. We have given that to DS before bed when we're concerned he may go low in the night.

kitedoc said:

So you are saying that the BSL definitely reaches peak 5 hours after eating carbs/fat and that the insulin only lasts 4 hours ???
What insulin may I ask??

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It doesn't peak, as in a spike. It rises slowly and steadily over a long period. Longer than the effectiveness of the insulin.
Novorapid.