Freestyle Libre Sensors in My Cats

Muffy’s Experience * Cat’s Experience * Oliver’s Experience* Lessons Learned

Two of my CKD cats, Muffy and Cat, also have diabetes. They had both been in remission with their diabetes until very recently. Now that their diabetes has returned I’ll be sharing our experience using the new Freestyle Libre implanted sensors for continuous blood sugar monitoring. Oliver is diabetic due to steroid use for another health condition.

Muffy’s Experience

Muffy’s diabetes came back, officially, in early July 2019. She was diabetic when I adopted her (August 2018) but went into remission after 3 weeks. She remained in remission until now through eating a low carbohydrate diet.

Recently, with some progression in her kidney disease I had to change her diet to one that is more protective of her kidneys, but that also makes it less appropriate for keeping her diabetes under control. So, now she is back on insulin.

Muffy is particularly offended by having her blood sugar tested from ear sticks, and HATES having her toes touched, so I’ve not even attempted the paw pad option. Because she has strong opinions and I like trying new gadgets to make my life simple, I opted for the Libre implant.

Implant Day One! July 17, 2019

**I was wrong in the video. I said it takes 12 hours for the sensor to calibrate. It only takes 1 hour.**

Muffy’s implant was placed on July 17 by the vet tech for the internal medicine (IM) doctor I use. This tech has a lot of experience with placing these sensors, and the IM vet herself is fantastic with old, sick kitties who are balancing CKD and diabetes.

Update: July 19

Muffy has been wearing the sensor for 2 full days now. She doesn’t seem to care about it at all. She scratches or grooms very lightly around the implant at times, but doesn’t try to remove it at all.

I’m obnoxiously following her around the house saying “let me scan you!” and she tolerates me with her normal grumpy affection.

Since having the implant in Muffy’s blood sugar has read “HI” almost exclusively (this sensor is only accurate 40 to 500 mg/dL).

After 2 days of wearing the sensor, and enduring a few additional ear pokes to confirm her levels, I believe one of our problems is that my insulin has gone bad. Muffy’s blood sugar has not been dropping at all, outside of the times of day when she isn’t eating or eats only low carb foods.

I purchased a new vial of Lantus this evening to give her the evening dose from a fresh bottle. I will know soon if the fresh insulin makes a difference.

End of the First Experiment

Tragically, late in the evening of July 19, Muffy got her sensor caught on the edge of the high-sided litter box. The sensor dislodged and cannot be reused.

Muffy will be getting a replacement implant and some T-shirts to wear with it, I’ve just got to work out a new schedule with her vet.

Stay tuned for more updates about Muffy…

Cat’s Experience

Cat’s sensor was implanted by his primary care (PC) vet on July 23rd. I went with the PC vet for this because she has been wanting to use these sensors for awhile, but hasn’t had any patients sign up to try them out. I’m willing, and I’ve got a diabetic cat in need of monitoring, so I elected to be their first for this implant. Unlike Muffy, Cat is perfectly content with having his ears poked for blood sugar testing, so his sensor is more about allowing my PC vet to gain experience with the technology.

Update: July 23

Fun Fact: If you look closely you can see Cat’s tabby stripes on his skin. Most “black” cats aren’t true black cats, and are black-on-black tabbies instead.

Cat’s sensor was implanted and the first thing I learned is that you must scan it immediately with your own reader device to activate it.

The tech from my PC vet’s office scanned the sensor with his phone, and by the time I left the office there were 20 minutes left before we could get the first reading.

Well, imagine my surprise when I got home and scanned it with my reader and found out I had to sit through the whole 1 hour calibration all over again!

For the rest of the day I was not able to get a real reading from Cat other than “LO,” meaning his glucose would be lower than 40 (the minimum number the sensor can read). Since Cat wasn’t comatose or having seizures it’s safe to say his blood sugar was higher than 40. I did an ear stick to confirm and his blood sugar was 235. Definitely more than 40.

Update: July 24

In the morning the sensor registered a reading, finally! But the reading was only 49… so, still reading too low.

After I came home from work the sensor registered “LO” then shut itself down for several hours to run some internal diagnostics. The sensor knew it was malfunctioning and needing to figure out if it could recover.

Well, the sensor could not recover, so it committed suicide instead. The internal diagnostics seem to have confirmed that there was no way the sensor would be able to give a reliable reading, so the program inside the sensor shut it down permanently instead.

I’ve decided to leave the sensor in place on Cat so that my vet can get an idea of how long the sensor will stay in place. His sensor is very securely fastened, so I won’t try removing it until it starts naturally loosening.

Update: August 3

Cat’s sensor finally came off today and I can see now why it was malfunctioning. The filament was very definitely bent during the initial installation and never made it underneath Cat’s skin to properly sample interstitial fluid.

In this first picture you can clearly see that the little filament tube from Muffy’s sensor is clean and sticking straight up – meaning it would have poked straight down into her skin while she was wearing it. On Cat’s sensor the little filament is barely visible in this photo but is bent at a sharp angle. When the sensor first came off the filament was stuck to the plastic disc completely and wasn’t even sticking out at an angle at all!

Side by side comparison of the sensors after removal

Here’s another view of those sensors. The arrows are pointing to the filament tubes that would have been collecting samples. In this picture you can more clearly see that Cat’s tube has glue around the outside of it. Muffy’s tube is hard to see because it’s standing straight up, but there’s no glue residue around the outside.

Another side-by-side comparison of the two sensors

In this next photo you can see where the sensor was attached to Cat. The arrow is pointing to where the filament from the sensor was sitting. You can clearly see in this photo that the filament had been bent during the initial placement and was lying across the top of his skin horizontally, rather than poking straight down into it. This placement also explains why the filament ended up with glue on it when it should not have been exposed to glue at all.

You can also see that the close shave Cat received was a bit too close. Although the glue from the sensor was already failing, and I was using an adhesive remover, he still has some minor abrasions to his skin from the removal process. It looks particularly bad in this photo because it’s such an extreme closeup.

Oliver’s Experience

Oliver’s sensor was implanted June 24, 2020 by his internal medicine vet, the same vet who applied Muffy’s sensor. Oliver successfully wore his sensor for 14 days. Actually, his sensor is still in place as of the writing of this update even though the sensor life ended 2 days ago. Oliver is a bit of a special case for me. He has become diabetic due to taking prednisolone (a steroid) to manage symptoms from collapsing trachea. Collapsing trachea is super rare in cats and treatment options are limited. Because of that Oliver can’t stop taking the steroid. For his treatment we are working on finding the lowest possible dose of steroid he can take while managing his symptoms from collapsing trachea. In the meantime we are also trying to find the appropriate dose of insulin to manage his glucose levels.

Oliver doesn’t like his sensor yet, so he gets to wear a fashionable tee shirt.

Here’s what 1 week of Oliver’s glucose levels look like. The purple dots are his actual readings during those time frames. As you can see, he does have a little bit of a curve, which is good, but his overall glucose levels are much too high.

Here’s what a single day of readings looks like. On this particular day I did manage to get his glucose down to the goal range for for a couple hours, but wasn’t able to keep it there.

After scanning his glucose sensor I had the option to add notes to the reader. In my scans before dosing insulin I did add his insulin dose as a note to the device, but I can’t find that information anywhere in the data that I’ve downloaded from the reader. It looks as though my notes on how much insulin was given and when Oliver took his prednisolone may be lost. I’m waiting on a reply email from tech support to find out if that’s true.

Lessons Learned

  • Do not install the sensor on an underweight/emaciated cat. There isn’t enough space in between their top layer of skin and their bones, and it’s likely that the capillary tube that’s used to sample the interstitial fluid is bent, blocked, or damaged by hitting against the underlying bone when it’s installed
  • Scan the sensor as soon as possible after it’s installed with your own reader device or phone if the vet doesn’t do that for you. The sensor won’t be activated to your reader until 1 hour after it’s scanned with your device.
    • If the sensor is initially activated by another person’s device you will still have to wait the full hour to start getting readings when you scan it with your own device
  • If you have high-sided litter boxes you may need to keep the sensor covered so that your cat doesn’t accidentally knock the sensor off when entering or exiting the litter box.
  • Do not inject insulin anywhere near the sensor. You can artificially lower the cat’s glucose readings if the insulin is too close to the sensor itself.
  • If your cat is receiving subq fluids, don’t place the needle for fluids too close to the sensor. The extra fluids can interfere with glucose readings for the entire time it takes for them to be absorbed.
  • If the sensor is reading HI or LO and not giving an actual number, do a manual blood sugar check to confirm your cat’s blood sugar level before administering any insulin.
  • Make sure you have some sort of adhesive remover on hand that is safe to use on cat skin. If the sensor partially dislodges you can damage your cat’s skin if you pull it away without dissolving any remaining glue first.