Libre 3 Inaccurate(?) and False Low Alarms - do I change the dose?

Kayleegoose

Kayleegoose

Member Since 2025
So I noticed a while back that my cat’s libre would say HI but when I tested him with the ReliOn, it would consistently be about 50 to 60 points lower. Fine, whatever it’s still high so didn’t worry too much about that.

Today it was showing his blood sugar dropping rapidly. All of a sudden it went from 120 to 66 and started sounding the low glucose alarm. I was obviously panicked and checked him a couple times with the ReliOn, which was around 230. I removed this libre and put a new one on which is now hovering around 250.

Added a screenshot of where we’re at now. Is this common? Was it just the sensor going bad? While it was dropping it gave me a sensor error and told me to check again in 10 minutes. It had 4 days left on it. I know all signs point to a faulty monitor but just wanted to see if anyone has had something like this happen, or if his glucose was dropping too fast and I need to adjust the insulin dose? Details in his sheet of dosage but I have no idea now if the recent numbers are accurate.
 

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Want to mention that the blanks in the spreadsheet are just because it was “HI” or 300+ the whole time. Just a few days ago we started seeing some change in the numbers so I started adding them again
 
Unfortunately this is one of the downfalls of the Libre sensors, aside of the fact that they sometimes stop working before the 14 days, and also fall off like magic, and the monitor won’t read numbers after 260 or so, they can make you have a nervous breakdown when that alarm goes off, the difference on BGs is real, most of our members use the ReliOn Premier human monitor and strip, much cheaper and reliable, and stress free😉, so if you stay with the Libre have some extra sensors handy ABBOTT will replace them but do not tell them is for your cat, and always keep the box of the sensor place, you’ll need it when calling for replacement, but if you see the monitor reading less than 90 please hand test to double check before giving carbs
 
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What food are you feeding your cat? Diabetic cats need to have a diet of wet can food between 0-10% carbs, kibbles or dry foods contain approximately between 20-30% carbs as well as dry treats, cats cannot digest carbs
 
CORKY said:
Unfortunately this is one of the downfalls of the Libre sensors, aside of the fact that they sometimes stop working before the 14 days, and also fall off like magic, and the monitor won’t read numbers after 260 or so, they can make you have a nervous breakdown when that alarm goes off, the difference on BGs is real, most of our members use the ReliOn Premier human monitor and strip, much cheaper and reliable, and stress free😉, so if you stay with the Libre have some extra sensors handy ABBOTT will replace them but do not tell them is for your cat, and always keep the box of the sensor place, you’ll need it when calling for replacement, but if you see the monitor reading less than 90 please hand test to double check before giving carbs
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Well that’s a bit comforting. So it likely wasn’t due to his glucose dropping too fast? We’re about one hour from his next shot and he’s still around 230. Should I decrease the dose so there isn’t such a dramatic drop?

Someone on reddit mentioned hair growing under the monitor can start to make it inaccurate, which I was surprised how much was under there when I removed it.
 
CORKY said:
What food are you feeding your cat? Diabetic cats need to have a diet of wet can food between 0-10% carbs, kibbles or dry foods contain approximately between 20-30% carbs as well as dry treats, cats cannot digest carbs
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He’s getting fancy feast pate and one can of Royal canin gastro food a day (which is around 5% carbs)
 
Ahhh! Is the Royal Cannin that’s keeping his BG high, did actually calculate the wet carb matter in this food? If you got this info from the vet,I question that in about an hour I will be sending you a link to a cat carb calculator, you will insert the nutrients %s as you see them in the calculator cells, the dry carb matter is what we are looking for. I do not give dosing advice, so I will tag a member that can assist you. Although we do not increase randomly according to th BG numbers, please hold a few minutes till someone plugs in
@Sienne and Gabby (GA)
@squeem3
 
CORKY said:
Ahhh! Is the Royal Cannin that’s keeping his BG high, did actually calculate the wet carb matter in this food? If you got this info from the vet,I question that in about an hour I will be sending you a link to a cat carb calculator, you will insert the nutrients %s as you see them in the calculator cells, the dry carb matter is what we are looking for. I do not give dosing advice, so I will tag a member that can assist you. Although we do not increase randomly according to th BG numbers, please hold a few minutes till someone plugs in
@Sienne and Gabby (GA)
@squeem3
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He’s been on that just over 2 weeks because we were in danger of megacolon. So slowly working him off of that. More concerned right now with him dropping too low, though. Carb count I got from this question and answer on the chewy page for the food:

What are the % of phosphorous, carb and protein on a dry matter basis in this food​

Answer by chewy • Jun 23, 2025
This recipe contains: 0.16% on an as fed basis and 1.02% on a dry matter basis of phosphorus, 5.37% on an as fed basis and 33.55% on a dry matter basis of carbohydrate, 6.69% on an as fed basis and 41.79% on a dry matter basis of protein.
 
if you do not see the nutrients, you can also go on CHEWY.COM look for the food on hand, click on the can, then scroll down, you will see ingredients, click on that, you will see the nutrients, those are the ones to place in the cells of the calculator, remember the dry carb % on the bottom right of the calculator is the Dry matter carb to look for, also the link to the Drs. food chart, the third column will have the % of carbs

Cat Food Nutrition Calculator | Elizabeth C Scheyder
https://catinfo.org/docs/CatFoodProteinFatCarbPhosphorusChart.pdf
 
if you need help if the BG drops lower than 70 please re do a thread post, titled it 911 LOW BG??, try to post ASAP it will get our attention immediately, I will have my phone on hand, I was told at the beginning these words "breath in breath out, cats are very sensitive to stress, you stress they stress" you are not alone, you are doing great! 🤗 🐱:cat::cat::cat:
 
ok. I have 13 minutes until I need to give his shot and ReliOn says he’s at 218. I’m afraid to give the 7.5 dose we’ve been doing for a few days. Hopefully someone can help soon.
 
Corky uses ProZinc and the protocols are different, and the numbers fluctuate with dosing, I shoot Corky in 70;s 80's but it takes a lot of practice to do that, I have never missed a dose, his BG is not low, then again the dose is huge, if you shoot, please test in two hours, and post the BG, and retest again in two hours at least for a bit, you do not want to be caught off guard. Do you have some Karo, or honey or high carb wet food on hand:? just in case we need to go down that path, relax we are here for you whatever you decide to do, remember that unfortunately, many members are either traveling or cooking for tomorrows holiday, but they always check the forum now and then, I am here I will do what I can if we need to act, just post the Bg here and on the SS, so we can catch it faster!
 
CORKY said:
7.5u is a lot of Lantus, did you increase on your own? I will do my best to get someone to plug in immediately, but next time give a bit more time, so testing like 1 hour before shot would be great, stall the shot for a bit, I cannot give dosing advice
@Diane Tyler's Mom GA
@Sienne and Gabby (GA)
@squeem3
@Wendy&Neko
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I’m using the tight regulation protocol. Wendy who you tagged advised me on this before and checked out his spreadsheet a little while ago. He wasn’t responding on the lower doses. Just confused what to do right now because it still seems to be dropping, even after feeding him dinner about 20 minutes ago and skipping the insulin dose
 
Kayleegoose said:
I’m using the tight regulation protocol. Wendy who you tagged advised me on this before and checked out his spreadsheet a little while ago. He wasn’t responding on the lower doses. Just confused what to do right now because it still seems to be dropping, even after feeding him dinner about 20 minutes ago and skipping the insulin dose
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Do you have medium carbs or high carb foods? Honey syrup? What’s he’s BG RIGHT NOW?
 
CORKY said:
Do you have medium carbs or high carb foods? Honey syrup? What’s he’s BG RIGHT NOW?
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It’s 224 right now. Which I understand is not too low, it’s just different from what I’ve experienced so far, so just wondering if I should do a lower dose. Wendy’s comments I mentioned were in another thread of mine.
 
I wish I can can help you with dosing it is not my place to do so, I do know that with ProZinc it is a great number to shoot,also it is no ok to reduce/increase at random according to the BG numbers, so far I have not seen any one plug in on this, do know I’m here is you decision, I will tag someone else right now too, do know I’m here do test every two hour after shooting for tonight so I can assist you in case tge numbers are too low post the BG NUMBER HERE PLEASE, the phone is right by my side face up for you we’ll work at it together
@Suzanne & Darcy
 
Not all cats react the same to insulin and you’re a newby, it is not wise for next time, but right now is desparete times, you did not say if you have the items You need to boost th BG if necessary? Post before you give any, that I can help you with right on point, please test in two hours post repeat
 
CORKY said:
Not all cats react the same to insulin and you’re a newby, it is not wise for next time, but right now is desparete times, you did not say if you have the items You need to boost th BG if necessary? Post before you give any, that I can help you with right on point, please test in two hours post repeat
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What’s not wise? I have Karo syrup and high carb food.
 
Comparing with other cats SS , I may be wrong, don’t quote me on that, but all cats react different to the insulin, in all cases you are doing great, you are brave, and you love York fur ball, so following your instinct is a good thing, Good job, I’m here
 
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@squeem3
Canyou you please plug in here and verify what I have posted Kaylee, I cannot give dosing advice, and she uses Lantus, help us out and review the posts if you can, and your input will be very much appreciated it😉
 
squeem3 said:
@Wendy&Neko was just around. 7.5 units is a lot. Have you asked the vet about high dose conditions like Cushing's or acromegaly?
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Below is a previous thread where I discussed the high dose with Wendy. I’ve been slowly increasing and not seeing any response until basically two days ago. Now I’m confused about what to do because normally he’s just “high” or 350+, especially at food time. It’s been about two hours since he ate and an hour and a half since insulin and he’s at 248. That’s only about 20 more than before his food and insulin which is just odd for what I’ve seen before. Now I’m afraid I gave him too much since everyone is saying it’s a lot. 11/10 Fluffy - All high and constipated
 
Is the Royal Canin dry or canned? If dry, that's probably the culprit in the high numbers. The canned is slightly better but some cats are super carb sensitive. The FF is just fine so you don't need to also feed Royal Canin.
 
squeem3 said:
Is the Royal Canin dry or canned? If dry, that's probably the culprit in the high numbers. The canned is slightly better but some cats are super carb sensitive. The FF is just fine so you don't need to also feed Royal Canin.
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It’s canned. You’re saying this could cause the high numbers and then the big drop?

I’m more worried about the numbers being low right now. I don’t know if I’m making sense since they’re still technically high. They’re just lower than normal for him and I’m afraid that if it stays around 248 then has another big drop like earlier it will be dangerous. I don’t know if that’s a valid concern. 7 units didn’t do anything before now.
 
Bgs are pink and yellow which is ok :) Bgs fluctuate all the time. I would be more concerned if bgs dropped from pink (or red or black) to green in a few short hours.

Maybe just feed only FF for a few days to see if that has any effect on bgs. There are lots of other low carb brands you can buy at pet stores and supermarkets. They're more affordable than the Royal Canin, too.
 
squeem3 said:
Bgs are pink and yellow which is ok :) Bgs fluctuate all the time. I would be more concerned if bgs dropped from pink (or red or black) to green in a few short hours.

Maybe just feed only FF for a few days to see if that has any effect on bgs. There are lots of other low carb brands you can buy at pet stores and supermarkets. They're more affordable than the Royal Canin, too.
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Ok, that makes me feel better thank you 😭 I think I’m still shaken up from the monitor telling that it did drop to the green and then to 66, when really it was at 230. We’re only doing the one can of Royal canin to help with constipation. I will slowly decrease it over the next few days to only have fancy feast
 
Kayleegoose said:
Ok, that makes me feel better thank you 😭 I think I’m still shaken up from the monitor telling that it did drop to the green and then to 66, when really it was at 230. We’re only doing the one can of Royal canin to help with constipation. I will slowly decrease it over the next few days to only have fancy feast
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For constipation you can purchase at any pharmacy over the counter MIRALAX, 1/4 tsp twice a day for 3-4 days, stop the ROYAL CANNIN, not only your cat will never regulate the BG, but is really not a great food to feed. Stick with FF pates, there are also some flakes like FF fish & shrimp flake, chicken chunky, cats that have been used to kibbles l love the chucks and they are 0-4% carbs, s e Corky’s SS , scroll to the left at the end is his menu, time and amount fed daily, both of my cats are very satisfied! And I feed less than 5% carbs, and you’re doing great, !
 
Kayleegoose said:
So I noticed a while back that my cat’s libre would say HI but when I tested him with the ReliOn, it would consistently be about 50 to 60 points lower. Fine, whatever it’s still high so didn’t worry too much about that.

Today it was showing his blood sugar dropping rapidly. All of a sudden it went from 120 to 66 and started sounding the low glucose alarm. I was obviously panicked and checked him a couple times with the ReliOn, which was around 230. I removed this libre and put a new one on which is now hovering around 250.

Added a screenshot of where we’re at now. Is this common? Was it just the sensor going bad? While it was dropping it gave me a sensor error and told me to check again in 10 minutes. It had 4 days left on it. I know all signs point to a faulty monitor but just wanted to see if anyone has had something like this happen, or if his glucose was dropping too fast and I need to adjust the insulin dose? Details in his sheet of dosage but I have no idea now if the recent numbers are accurate.
Click to expand...
Are you using a Libre 3? They just sent out an urgent alert yesterday www.FreeStyleCheck.com -not sure it's related but good to know about regardless.
 
This is a great article, and it was about time it was released! Thank you, this is why we always urge our members using the Libre that in Low BGs to also retest with a human monitor, thank you for the article❤️😉
 
Sorry about being late, was bogged down in a zoom on organizations bylaws. 😴

I think you can go back to 7.5 units tomorrow morning. He was just starting to see better numbers. It's not uncommon for the Libre to test lower than the human meter in lower numbers.
 
Wendy&Neko said:
Sorry about being late, was bogged down in a zoom on organizations bylaws. 😴

I think you can go back to 7.5 units tomorrow morning. He was just starting to see better numbers. It's not uncommon for the Libre to test lower than the human meter in lower numbers.
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Thank you Wendy 🙏 my biggest concern was the big drop. I’m guessing it was from 350 to 230 earlier? Guessing 350 based on the inaccurate libre numbers. Do I need to be afraid of a sudden drop again into a danger zone? We’re 2.5 hours post insulin and he’s down to 201. I’m just not used to seeing this at all.
 
@Wendy&Neko
I’m more relived now, thank you Wendy, I feel more relived now, I tried to help to the best of my ability without giving any dosing advice, now I can rest, The phone has been glued to my hand, I know how it feels being scared and desperate, when we are new to FD. And not knowing what to do, ❤️😉
 
That 201 is probably from the 7.5 unit depot. He may drop a little more, but then head back up. What you want eventually is numbers mostly in the blue and green range. Paws crossed the first of those blues shows up soon. If it does, and you are awake, double check with the Relion if you can, so you get a better idea how the two compare in slightly lower numbers.
 
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