GRRR. I just typed you a longish message on my phone, and my login timed out. I lost it! Here I am on the laptop at home.
Sorry if this is long and repetitive. I want to clarify for you and get to work on the tons of things I gotta do today, but I don't want to leave you confused.
Sorry to be unclear. When I began to give Max insulin and test his BG, I found it so hard to figure out what was important at the beginning of his care. I saw what other people were doing, and I didn't know if they did those things because it was absolutely necessary for all diabetic cats or whether they were doing those things because they were fine-tuning their care of their cats in ways that weren't necessary for me until I was ready to do them. I wanted to take care of Max perfectly, and yet I began to realize pretty quickly that there was a threshold of care that was required, and that there were other things that would be useful later on. Some of those things were "required" for a newly diganosed cat who dropped in the below 200 range just from a change in his food alone. For my cat, they were optional until his BG got close to 200 at pre-shot.
Eventually, you will want to use a feeding schedule when your cat's BG gets lower overall. For now, the only "rule" is to make sure he's eaten sometime close to the time directly before the shot. A lot of people like to withhold food for 2 hours prior to the shot so that they know the BG test they get is not due to food the cat ate within that 2 hour period prior to the shot. (Some withhold food for 4 hours or even 6.) Then, they test, feed, shoot in that order. This is to make sure that the cat doesn't get an insulin shot and then refuse to eat. if the cat has decided he doesn't want to eat for the next 4 or 5 hours, the insulin would not have any food to counteract it's effect, and the BG could drop too low.
Right now, just make sure you test first, then feed and see that the cat is willing to eat (or know what time he last ate and that is was within an hour or so of the pre-shot test), and then shoot. Sometimes the food is there on the floor, and he eats it at +11. Then he isn't very hungry at shot time. You don't want to miss a shot just because he won't eat because you know he ate not long ago and that is why he isn't hungry. You can put some food on a spoon and put it to his mouth a couple of times to get him to want it. Rub it on his paws or something like that if you feel better having done that. What you want to avoid is a cat who is refusing food, eating very little if at all, and refuses to eat when his BG is high, but he gets an insulin shot anyway. That could send him into a low blood sugar problem.
If his BG is high, he should be hungry most of the time, and should be willing to eat just about anytime you offer it. If he won't eat, something is wrong. If you are at all worried that your cat is not eating well or refusing food, giving insulin can be dangerous. Please post for advice. It's a delicate balance when you are worried about ketones and you know the cat needs insulin and yet you are worried about giving insulin when it might cause the BG to drop too low, etc.
For the future, knowing that the BG test pre-shot is not influenced by food is especially important if the cat's BG is hovering around 200 at shot time for a newly diagnosed cat whose owner does not yet have a decent amount of data on the cat's response to insulin. Later on it becomes important at every shot time when the cat is hovering at about 100 or even 150 maybe. When you are in the 400s, it's nice, but not necessary in most cases, to gather information by withholding food for 2 to 4 hours prior to shot, or even from nadir to shot time. Each cat responds differently to food and insulin, thus the varying periods of time to withhold food. The data you gather will help you when the pre-shot starts to get to around 200.
If you have the time and energy, there is no reason to not start feeding on a schedule and gather this data now. Your cat might suddenly have a radical change in his artificial insulin needs, and you will wish you had been doing this all along. Nonetheless, if you are starting to feel overwhelmed or frustrated, then, when your cat's BG is in the 400s at pre-shot, what time you allow him to eat food prior to the pre-shot TEST is less important than watching for ketones, watching for refusal to eat, and other unusual behaviors like peeing outside the litter box or throwing up. As long as you are aware that if his BG at pre-shot is under 200, you should not give him a shot without advice from someone who has the knowledge to help you decide.
A BG of 400 at pre-shot is at a very safe level for giving a shot (unless the cat has a very unusual response to insulin). So, if it's 400 or 450, it doesn't matter if the glucose in the blood is because he ate at +10.5 or +11 or +11.5. It's high enough that you are seeing a need for insulin. This is why I say it's okay for him to eat prior to the shot right now if you can't absorb all this information, try to adjust your life to this new responsibility, handle the stress of caring for him, suffer from getting up in the middle of the night, etc. etc. because his BG is pretty high as it is. It's not "ideal" that he may be having "food spikes" at pre-shot, but I don't want to overwhelm you by suggesting that you worry about that now in comparison to everything else you are handling (quite well, by the way).
Does that make more sense? If you see a pre-shot of 200 or below, please don't give a shot. Please post for advice and let someone help you decide how to handle the situation after he/she has looked at your SS to see what he/she can tell you about whether you have enough data to "shoot below 200." (Not me, by the way, I'm still learning that sort of stuff, and I want reinforcement that I'm okay to shoot at pre-shot sometimes myself.) Just trying to impart some of what I've learned and "pass it on."