Newly Diagnosed - Advice on CGM and Hypoglycemic Reaction

C

CocolovesCooper

Member Since 2026
Post Title: New here — 10 days in, CGM failures, hypoglycemic crashes, neuro symptoms now resolved — need guidance​


Hi everyone. I found this community while researching options for my cat Coco, who was diagnosed with diabetes and pancreatitis 10 days ago. I’m overwhelmed and trying to get my footing so I can care for her without causing her more stress. I have two main questions and would be so grateful for any experience or guidance.

About Coco
11-year-old Siamese, diagnosed 10 days ago with diabetes and pancreatitis. She currently weighs 6.3 pounds with significant muscle wasting — very underweight. She had a UTI (treated with antibiotics) which, along with the pancreatitis, caused her to stop eating for three days - I thought I was going to lose her, but she turned the corner and started eating (although small amounts) so vet started diabetes treatment. Her insulin is Vetsulin, 1 unit every 12 hours. The weight loss seemed to happen quickly, and I carry a lot of guilt about not getting her to the vet sooner. I’m sharing this not for reassurance but because I want to be honest about where we’re starting from.


Question 1 — CGM reliability on a thin cat, and whether to switch to a regular glucometer​

My vet has placed two FreeStyle Libre 3 sensors on Coco. Both failed.

The first sensor was working until the vet administered subcutaneous fluids, after which it stopped reading immediately. The second sensor was placed yesterday and has never worked at all — no readings from the start.

I’ve since read that CGMs may not be reliable on very thin or underweight cats because there isn’t enough subcutaneous space for the filament to sit correctly. Is this consistent with others’ experience? Has anyone had reliable success with the Libre 3 on a thin cat?

I really don’t want to keep bringing Coco in for sensor application and removal — it’s stressful for her and they keep failing anyway. I’m considering switching to a regular home glucometer and have been looking at the PetTest system. Do others find this more reliable for day-to-day monitoring? How often do you test, and what site works best — ear vein or paw pad?

Question 2 — Severe hypoglycemic crashes, and neurological symptoms that have now resolved​

After Coco’s very first dose of Vetsulin (1 unit), her glucose dropped dramatically from the 400s to the high 60s. I applied honey to her gums as directed and her glucose recovered to above 350.

At the second dose 12 hours later, the same crash happened but more quickly. When her reading hit 85 I applied sugar proactively. Her glucose came back up — but about 30 minutes later Coco began stumbling, tilting her head to one side, and walking very abnormally. This continued for three days before slowly subsiding.

I brought her to the vet yesterday and she was examined — the neurological symptoms have cleared and she is doing much better. But I’m wondering what the community thinks may have caused this. Was it likely hypoglycemic damage to the brain, or could something else explain it? And has anyone experienced this with Vetsulin at this dose in a thin cat — is 1 unit possibly too high for her?

Because the second sensor has never worked, I currently have no glucose reading and am hesitant to give another insulin dose without knowing where her levels are. What would people do in this situation?

Thank you so much for reading all of this. I’m trying to learn quickly because Coco deserves better than these first 10 days have been. Any guidance is welcomed!
 

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Welcome to FDMB!

I'm providing a link to a post on CGMs. In addition, there are several members who are experiences with their use:
The post also provides a link to a Facebook group that is for pet owners using CGMs. There are instructions on how to replace the sensors. I never used a CGM so I can't comment on whether their use is compromised in a cat that's underweight. However, we also have lots of information on home testing with a hand held glucometer. The CGMs tend to provide inaccurately low results if your cat's blood glucose is under 100 so we encourage members to learn how to manually home test. Many members use the Walmart Relion meter. The strips for this meter are among the least expensive available which contributes to it's popularity. However, any human meter is fine and the strips will be far less expensive than strips for a pet-specific glucometer.

You might want to discuss the use of Vetsulin with your vet. It is an insulin that is no longer recommended by the American Animal Hospital Association due to it working quickly and not lasting 12 hours. Vetsulin tends to be harsh and drop numbers hard and fast. The two typed of insulin that are recommended for treating feline diabetes are Prozinc and Lantus (glargine). These are gentler and have a longer duration.

Given that Coco is underweight, a smaller dose of insulin may be warranted. Generally, with the dosing approach we use, a drop to 60 on Vetsulin would indicate that the dose is too high. Dropping it back to either 0.5u or 0.75u should be a consideration.
 
Welcome to FDMB
Coco is beautiful, It is overwhelming and we all feel guilty, but you are not alone, we have all been there, cats hide illnesses quite well, and unless you are familiar about the signs for Feline diabetes, like I was not, it does catches us by surprise. We are here to help
Question 1
The CGM Libre, you have experience one of its flaws, and is not just on thin cats, when Corky left the hospital he left with a sensor, it fell off by nighttime, he weight 8.5lbs from 16.5lbs, you do not need the vet to replace them, you can do it yourself get a prescription with many sensor refills, keep a couple handy at home, the sensors are expensive plus adding up the vet visit, the replacement and charging extra for the sensor, it can become quite expensive every 14 days, Most members use the ReliON Premier human monitor and strips, if you are in US (Walmart )or any human brand will do, no need to spend on an expensive Pet meter either.
Question 2
The best insulins for cats are ProZinc and Lantus they are a 12-hour insulin easy on the cat, Vetsulin / Cannisulin, is a dog insulin that hits hard and fast in a cat, the symptoms you are describing are of a hypoglycemic episode, you were not testing before shot, the glucose level could have been low, by giving the insulin without testing this is the result, and it is dangerous. I can advice for you to see the vet and strongly request to switch insulins, as well as to start Coco on a low dose, that after what you experienced with the hypo episode you want to take it slow until you feel comfortable purchase a human meter and strips every meter has its own strips) always have extra strips handy,
HYPO KIT, please have these items always handy in case of need: a few cans of medium carb food between11-15 carbs, some high carb food between 16-24% carbs, some Karo syrup or honey, these last two are used when BG is under 50, they are only a quick fix, so is best to raise the BG with food first a non diabetic cats' glucose level is between 50-120

if Coco only has diabetes and no other major illnesses, you can handle Coco's diabetes right here, we can assist you with dosing as well, your vet may refer to you about a curve, this also does not need to be done at the vets office, is simply testing every 2-3 hours for a cycle (12hours), cats are very sensitive to stress, so the glucose levels at the vet will not be realistic, that may cause an unnecessary dose increase.
A diabetic cat needs to have a diet of wet can or raw food between 0-10% carbs, Most members feed Fancy Feast or Friskies, most feed up to 5% carbs, if you are feeding kibbles (dry food) the transition needs to be a slow on, not to upset Coco's stomach as well as since the dry foods contain between 20-30% arbs, by suddenly giving low carbs it will cause for the glucose level to spiral down, so home testing is very important in all aspects. below are several links, a Drs approved food list with many brands to choose from, the third column has the carb % for each food, we are also very numbers oriented, we would like you to create your signature and Coco's spreadsheet, this way we can all be on the same page links below, keep posting, we are here for you

Sticky - New? How You Can Help Us Help You!
https://felinediabetes.com/FDMB/threads/how-to-create-a-spreadsheet.241706/
Info - Dr. Pierson - new Food Chart
 
Sienne and Gabby (GA) said:
Welcome to FDMB!

I'm providing a link to a post on CGMs. In addition, there are several members who are experiences with their use:
The post also provides a link to a Facebook group that is for pet owners using CGMs. There are instructions on how to replace the sensors. I never used a CGM so I can't comment on whether their use is compromised in a cat that's underweight. However, we also have lots of information on home testing with a hand held glucometer. The CGMs tend to provide inaccurately low results if your cat's blood glucose is under 100 so we encourage members to learn how to manually home test. Many members use the Walmart Relion meter. The strips for this meter are among the least expensive available which contributes to it's popularity. However, any human meter is fine and the strips will be far less expensive than strips for a pet-specific glucometer.

You might want to discuss the use of Vetsulin with your vet. It is an insulin that is no longer recommended by the American Animal Hospital Association due to it working quickly and not lasting 12 hours. Vetsulin tends to be harsh and drop numbers hard and fast. The two typed of insulin that are recommended for treating feline diabetes are Prozinc and Lantus (glargine). These are gentler and have a longer duration.

Given that Coco is underweight, a smaller dose of insulin may be warranted. Generally, with the dosing approach we use, a drop to 60 on Vetsulin would indicate that the dose is too high. Dropping it back to either 0.5u or 0.75u should be a consideration.
Click to expand...
Hello and welcome. Glad you are here and we would love to help you with Coco!

I am a long time user of a Libre 3. I do not have experience with a very thin cat so I can’t answer that question about a CGM’s ability to work on a thin cat. However, the Facebook group Freestyle Libres for Dogs and Cats has many members and can most likely answer these questions.
Please read the link Sienne provided above, we have loads of food information in there about using a Libre sensor!

I do know that if your vet is using glue to adhere the Libre (please do not allow them to do that as it kills the sensor and it won’t work).
Also, it is recommended that subcutaneous fluids be given on the Opposite side of the body as the sensor is sitting. The fluids also ruin the sensors and won’t give accurate readings at all and will most likely shut down the sensors anyway.

The sensors are easy to apply and remove yourself, if you will use them (always have SEVERAL extras on hand at home) as they can fail at the worst time when you can’t get more from the pharmacy.

They can’t read incorrectly when the Libre reads under 100 or LO (the lowest readings under 40)
So it’s best to be able to double check with a blood test (ear prick) to make sure your cat is safe.

If you can or want to use a handheld meter, it’s most accurate, but some cats (like mine) won’t allow constant ear pricks. She’s a fractious cat but I can test her when she’s very low (not an every day occurrance).

It does sound like the dose of Vestulin is too high and it’s best to use Lantus or Prozinc for cats anyway.

I hope this helps, please let us know if you have more questions! 💖
 
Sienne and Gabby (GA) said:
Welcome to FDMB!

I'm providing a link to a post on CGMs. In addition, there are several members who are experiences with their use:
The post also provides a link to a Facebook group that is for pet owners using CGMs. There are instructions on how to replace the sensors. I never used a CGM so I can't comment on whether their use is compromised in a cat that's underweight. However, we also have lots of information on home testing with a hand held glucometer. The CGMs tend to provide inaccurately low results if your cat's blood glucose is under 100 so we encourage members to learn how to manually home test. Many members use the Walmart Relion meter. The strips for this meter are among the least expensive available which contributes to it's popularity. However, any human meter is fine and the strips will be far less expensive than strips for a pet-specific glucometer.

You might want to discuss the use of Vetsulin with your vet. It is an insulin that is no longer recommended by the American Animal Hospital Association due to it working quickly and not lasting 12 hours. Vetsulin tends to be harsh and drop numbers hard and fast. The two typed of insulin that are recommended for treating feline diabetes are Prozinc and Lantus (glargine). These are gentler and have a longer duration.

Given that Coco is underweight, a smaller dose of insulin may be warranted. Generally, with the dosing approach we use, a drop to 60 on Vetsulin would indicate that the dose is too high. Dropping it back to either 0.5u or 0.75u should be a consideration.
Click to expand...
Thank you so much! This is very helpful and the insulin switch recommendation was echoed in another response. I will ask my vet, but she is somewhat rigid in her thinking and so far has provided advice inconsistent with that found on vet sites and forums such as these. In any case, I appreciate your thoughtful response.
 
Staci & Ivy said:
Hello and welcome. Glad you are here and we would love to help you with Coco!

I am a long time user of a Libre 3. I do not have experience with a very thin cat so I can’t answer that question about a CGM’s ability to work on a thin cat. However, the Facebook group Freestyle Libres for Dogs and Cats has many members and can most likely answer these questions.
Please read the link Sienne provided above, we have loads of food information in there about using a Libre sensor!

I do know that if your vet is using glue to adhere the Libre (please do not allow them to do that as it kills the sensor and it won’t work).
Also, it is recommended that subcutaneous fluids be given on the Opposite side of the body as the sensor is sitting. The fluids also ruin the sensors and won’t give accurate readings at all and will most likely shut down the sensors anyway.

The sensors are easy to apply and remove yourself, if you will use them (always have SEVERAL extras on hand at home) as they can fail at the worst time when you can’t get more from the pharmacy.

They can’t read incorrectly when the Libre reads under 100 or LO (the lowest readings under 40)
So it’s best to be able to double check with a blood test (ear prick) to make sure your cat is safe.

If you can or want to use a handheld meter, it’s most accurate, but some cats (like mine) won’t allow constant ear pricks. She’s a fractious cat but I can test her when she’s very low (not an every day occurrance).

It does sound like the dose of Vestulin is too high and it’s best to use Lantus or Prozinc for cats anyway.

I hope this helps, please let us know if you have more questions! 💖
Click to expand...
Thank you Staci and Ivy! Really helpful information. The vet used glue to apply, so it sounds like this might be the issue. If I can get the CGM to work, I do think it would be a better option for Coco than ear pricks as I don't know that she will tolerate (although I will try). May I ask - what is the best way to remove the non-working Libre monitor the vet attached yesterday? I really don't want another trip to the vet just to remove it - she's had 5 vet visits in the past 12 days!
 
CORKY said:
Welcome to FDMB
Coco is beautiful, It is overwhelming and we all feel guilty, but you are not alone, we have all been there, cats hide illnesses quite well, and unless you are familiar about the signs for Feline diabetes, like I was not, it does catches us by surprise. We are here to help
Question 1
The CGM Libre, you have experience one of its flaws, and is not just on thin cats, when Corky left the hospital he left with a sensor, it fell off by nighttime, he weight 8.5lbs from 16.5lbs, you do not need the vet to replace them, you can do it yourself get a prescription with many sensor refills, keep a couple handy at home, the sensors are expensive plus adding up the vet visit, the replacement and charging extra for the sensor, it can become quite expensive every 14 days, Most members use the ReliON Premier human monitor and strips, if you are in US (Walmart )or any human brand will do, no need to spend on an expensive Pet meter either.
Question 2
The best insulins for cats are ProZinc and Lantus they are a 12-hour insulin easy on the cat, Vetsulin / Cannisulin, is a dog insulin that hits hard and fast in a cat, the symptoms you are describing are of a hypoglycemic episode, you were not testing before shot, the glucose level could have been low, by giving the insulin without testing this is the result, and it is dangerous. I can advice for you to see the vet and strongly request to switch insulins, as well as to start Coco on a low dose, that after what you experienced with the hypo episode you want to take it slow until you feel comfortable purchase a human meter and strips every meter has its own strips) always have extra strips handy,
HYPO KIT, please have these items always handy in case of need: a few cans of medium carb food between11-15 carbs, some high carb food between 16-24% carbs, some Karo syrup or honey, these last two are used when BG is under 50, they are only a quick fix, so is best to raise the BG with food first a non diabetic cats' glucose level is between 50-120

if Coco only has diabetes and no other major illnesses, you can handle Coco's diabetes right here, we can assist you with dosing as well, your vet may refer to you about a curve, this also does not need to be done at the vets office, is simply testing every 2-3 hours for a cycle (12hours), cats are very sensitive to stress, so the glucose levels at the vet will not be realistic, that may cause an unnecessary dose increase.
A diabetic cat needs to have a diet of wet can or raw food between 0-10% carbs, Most members feed Fancy Feast or Friskies, most feed up to 5% carbs, if you are feeding kibbles (dry food) the transition needs to be a slow on, not to upset Coco's stomach as well as since the dry foods contain between 20-30% arbs, by suddenly giving low carbs it will cause for the glucose level to spiral down, so home testing is very important in all aspects. below are several links, a Drs approved food list with many brands to choose from, the third column has the carb % for each food, we are also very numbers oriented, we would like you to create your signature and Coco's spreadsheet, this way we can all be on the same page links below, keep posting, we are here for you

Sticky - New? How You Can Help Us Help You!
https://felinediabetes.com/FDMB/threads/how-to-create-a-spreadsheet.241706/
Info - Dr. Pierson - new Food Chart
Click to expand...
Good morning Corky's parent, Thank you for your thoughtful reply. I had a reading on the CGM (the first one worked until the vet gave fluid and it deactivated). She was somewhere above 350 (this is a highest level the monitor will report) and fell to low 60s fairly quickly. So, yes, a definite hypo crash regardless. I have requested replacement CGM from Abbott and can try again, while starting to test with ReliON in the meantime. I will also request a change in insulin. The vet I'm seeing (while trying to find a new one) is very hesitant to listen to my requests so may poo-poo a change in insulin. I will be persistent though. The crash on Sunday was so scary and I believe Coco really suffered for the next 72 hours. Thank you also for your advice on food - she is a wet food girl and loves fancy feast. My vet actually told me to switch to dry food!!! I knew this was incorrect and brought up the carbohydrate levels in dry food. She proceeded to talk about the difference between simple and complex carbs (ugh). In any case, it's clear that I need to do my own research, use common sense, advocate for Coco...and find a different vet!
 
CocolovesCooper said:
Thank you so much! This is very helpful and the insulin switch recommendation was echoed in another response. I will ask my vet, but she is somewhat rigid in her thinking and so far has provided advice inconsistent with that found on vet sites and forums such as these. In any case, I appreciate your thoughtful response.
Click to expand...
Actually is not how rigid your vet can be, it is what it is, Caninsulin is a dog insulin, dogs do not have the same system, you want what is best for Coco, hypoglycemia is not a pretty site, and very dangerous for Coco, let her know you are going o be home testing, she might argue about that, but that is what any person or animal on insulin needs, and to start you on a low dose, you want to see how the insulin works in Coco's system, every cat is different reacts differently to insulin, and you need to adjust to this new journey yourself, what is best for Coco and more comfortable for you is more important than the Vet's comfort, you are in control, you are with Coco and know Coco more than your vet does, follow your instincts, they never fail and constant vet visits, will break your pocket and stress Coco, aside from the possibility of a hypo episode, I do not give dosing advice, but the members that do always like to start with a low dose it takes between 2-3 cycles days) to really understand how the insulin is working, and the increases/decreases should be done with 0.25 units at a time, It really works! I trust this Forum and their members blindly, today Corky is very Tightly Regulated, (see Corky's Spreadsheet, below in blue,) where he began in 2023 to today, a non diabetic cats' glucose level is between 50-120!
he is on ProZinc, unfortunately he is one cat that will be a lifetime diabetic, health as can be. but all his recovery has been done right here, this forum saves cats lives, by the way I have a 1/2 Main Coon female named Coco as well ;) 🤗
 
CocolovesCooper said:
Thank you Staci and Ivy! Really helpful information. The vet used glue to apply, so it sounds like this might be the issue. If I can get the CGM to work, I do think it would be a better option for Coco than ear pricks as I don't know that she will tolerate (although I will try). May I ask - what is the best way to remove the non-working Libre monitor the vet attached yesterday? I really don't want another trip to the vet just to remove it - she's had 5 vet visits in the past 12 days!
Click to expand...
Yes, you can use organic coconut oil on a q tip and very gently go round and round the adhesive paper which attaches the sensor to their skin.
Or use Brava spray, bought on Amazon (see the Libre user document we’ve linked for lots of information on this and more)
If it won’t lift off easily you may need to do several attempts to get one of these to “soak” into the glue to loosen it up.
Never pull it off as it can damage their fragile skin.

It’s why we tell users never to allow the vets to use glue.
But when you are just starting out, you would not know that and we trust the vets to know what to do. Unfortunately, they just really don’t when it comes to Libres. They are not really trained in how to use a libre since it is not intended for pets.
The best way to keep the sensor on if your cat will want to pull it off is to keep it covered and again we go over different ideas of what to do about that in the document.
And lots more information on the Facebook group regarding these situations.
 
CocolovesCooper said:
Good morning Corky's parent, Thank you for your thoughtful reply. I had a reading on the CGM (the first one worked until the vet gave fluid and it deactivated). She was somewhere above 350 (this is a highest level the monitor will report) and fell to low 60s fairly quickly. So, yes, a definite hypo crash regardless. I have requested replacement CGM from Abbott and can try again, while starting to test with ReliON in the meantime. I will also request a change in insulin. The vet I'm seeing (while trying to find a new one) is very hesitant to listen to my requests so may poo-poo a change in insulin. I will be persistent though. The crash on Sunday was so scary and I believe Coco really suffered for the next 72 hours. Thank you also for your advice on food - she is a wet food girl and loves fancy feast. My vet actually told me to switch to dry food!!! I knew this was incorrect and brought up the carbohydrate levels in dry food. She proceeded to talk about the difference between simple and complex carbs (ugh). In any case, it's clear that I need to do my own research, use common sense, advocate for Coco...and find a different vet!
Click to expand...
Make sure that when you call ABBOTT for sensor replacement not to say is for your cat or they will not replace them also keep the box of the sensor placed in case you need to replace it, there are serial numbers and other information on the back of the box they will ask you for, and always have at least 2 handy ABBOTT takes about 48-72 hours before you receive it, replacing it, is a walk in the park, you do have to re-shave the area where the sensor was removed. Corky used the Libre the first few months and I replaced them all the time ,,it’s a breeze
 
Last edited:
In regards to question 1: I did not have a good time with the Libre 3 sensor. My vet says it is better for tracking overall blood glucose trends, the numbers that it reads are not minute-by-minute they are delayed because they test within the muscle rather than the blood stream. Both Libre 3 sensors that have used so far also had issues with compression lows, ie., when the cat lays on that side or rolls, and it causes a false low alarm. I did not get much sleep those weeks because as soon as the cat rolled over in her sleep, it sent out the emergency low alarm. I would rush to test her, only for her glucose to be perfectly fine, and by the time I looked back at the app, the cat was sitting upright and the reading had gone back to normal. It is good insight for the overall trends, but keep in mind that those instant readings may be inaccurate, so I would recommend if any reading looks funny, do a manual meter test to see what's up.
I use the Keto Mojo handheld because it can do ketones and sugar in the same monitor. I test ketones once a day, and glucose several times a day, at least. I test each time before I leave the house, before I give her the Bexacat pill, and I test a few hours after the pill and/or before bed (usually the same time). I will also test both ketones and glucose more frequently if she is behaving weird at all. I poke on the outside edge of her ears because she hates having her feet touched. I kid you not she behaves worse at the vet when getting her nails trimmed than for any other procedure or exam of any kind.
 
You are doing a great job!! And congrats on switching from Libre to hand held monitoring, I went thru a lot of sleepless nights and hair pulling myself! I see lots of blues that’s great soon you’ll may start to see greens which is great! Good job!! I personally never even thought of the idea of pinching Corky’s paws, he’s already traumatized since I adopted him at 10 weeks old from the shelter, the monsters that turned him in had de-Clawed him! I took him with front paws bandaged! 😉
 
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