Ideally you prick between the edge of the ear and the vein. If you hit the vein itself, no big deal. Most cats will get a hematoma from pricking but apply firm pressure to the ear with a tissue after pricking to help stop the bleeding and minimize a hematoma.
Well, I just did that but by the hand, as using the prick pen it's kinda difficult to hit that small spot and it worked from the first try
What is the name of the insulin?
I hope the 40 UI is a type. Do you mean 4 UI / units?
It's Caninsulin 40UI/1ml
Well, I live in Romania so I guess the measure values are different from country to country, I meant to say 40 Units / 1ml of insulin
Wait.... you're giving insulin every 6 hours? Did the vet tell you this? Insulin is given every 12 hours for cats. There may be some rare exceptions.
Insulin works by lowering blood glucose levels so yes you should see numbers dropping when you test

A cat's blood glucose numbers vary every single day just like it does with Human diabetics.
Yes, the vet told me to give him insulin every 6 hours as the BG is not dropping that good, like, this morning he had "HI" again, which is somewhere around 600 mg/dL, the vet told me to use the >360 2UI of insulin and <360 1UI of insulin, 2UI of 40UI insuline it's somewhere like 0.05ml in a 100UI syringe, unfortunately in my country I'm not able to find the 40UI syringes so I have to convert from 40UI to 100UI by multiplying the dosage with 2.5, so basically I have to give him 0.02ml of 40UI insulin, but have to put 0.05 in a 100 Syringe as the gradations are different
I give him 3 times a day the insulin because if I give him 2 times, in the morning at 7AM the glucose meter shows "HI" and at 7PM shows "HI" as well, so vet told me to check his BG every 6 hours in the day, and give him 2UI/0.02ml of insulin everytime his BG is above 360 mg/dL and 1UI/0.01ml if his BG is under 360mg/dL but higher than 160mg/dL
The canned is better than the dry. Dry food keeps blood glucose levels too high. Before you ditch the dry food, get comfortable with testing your cat's blood glucose levels and understand how the insulin works for your cat. There may be better quality canned foods than the Royal Canin. What country are you in?
I live in Romania, I know that canned food works better but it's kinda expensive here, it's somehwere like 1.26 Euro per 80g, and that's kinda expensive in my country which the minimum wage is 400 Euros, vet recommended me Royal Canin for diabetic cats, both dry and wet food, I give him sometimes wet food as well but trying to reduce the costs as everything about this disease is pretty expensive here
So PMPS (PM pre shot) 366 and +6 was 330. That's a nice drop

Where are you seeing increasing numbers? A fur shot may result in increasing numbers.
I don't know how nice is that drop as it's in mg/dL, the normal values should be somewhere between 50 and 160 mg/dL, the thing was that a few days ago, on the last PMPS of the day he had 190 mg/dL, and on friday he had 366, the numbers are decreasing over the day, but everytime in the morning his BG is >600 mg/dL and that's why I don't know why it's happening, I don't let the food there over night, I just feed him after the insulin shot and that's it.
I mean, I know that everything under 300 it's in the "Yellow zone" if I'm not mistaken, but he mostly achieve the under 300 mg/dL close to the evening, also sometimes he got under 300mg/dL on PMPS of the 1PM and that's great, but it's not always like that
Can you set up a spreadsheet and input all of your cat's blood glucose numbers? The instructions are here:
https://www.felinediabetes.com/FDMB/threads/how-to-create-a-spreadsheet.241706/ FDMB members can better help you if you have a spreadsheet.
I'll try to do the spreadsheet as I have the values saved on glucose meter app on my phone, thanks for the reply.
Now you can see the variations of BG from a day to another I'm talking about
Later edit: I have done the spreadsheet at put it into my signature, I hope I understood well the values in the spreadsheet, also I had 3 days where I wasn't able to give him 3 shots because of my working schedule
I would also like to upload a photo of the treatment scheme that I'm currently using, it was made before the decision to give him 3 shots per day but I'm using the same scheme

"1 UI de doua ori pe zi" means 1UI two times a day
"2 UI de doua ori pe zi" means 2UI two times a day
I'm basically following the 1UI for <360mg/dL and 2UI for >360mg/dL but three times a day instead of two, also the vet told me his BG is under 160mg/dL to don't give any insulin
Later Later Edit: I also thought of giving him one day only canned food to see if it improves the BG over that day