Carol -
The Hill's products, even the "diabetic" diet, are fairly high in carbs. If you're feeding the canned M/D, it's 14% carb -- what we'd consider a medium carb food. If your vet is insisting on a prescription canned food, the Purina D/M is 7% carb. Neither of these brands has impressive ingredients -- they are mostly animal by-products vs. muscle meat. The raw foods that are commercially prepared here in the US are all very low in carbs and would be a better choice than a 14% carb food. I know there are members in the UK who have found canned foods that are low in carbs. You may want to post on the Health board here and ask about foods that are available in the UK.
You might want to think in terms of calories per day vs. the amount of food you're giving. Calories can really vary from product to product. Dr. Lisa's website on
feline nutrition has a formula for calculating the approximate calories per day for your kitty:
Required calories per day = [13.6 X optimal lean body weight in pounds] + 70
She notes that this is a "generous" calculation so if Carbonel needs to gain weight, it may be fine or you may want to provide more calories than what's noted given what would be a good weight for Carbonel.
Thanks for updating Carbonel's SS. On the days when you don't have an AM dose listed, did you skip the shot?
You're correct in that if a cat is in consistently good numbers you can hold the dose. If a kitty is in normal numbers (50 - 120) for a week, you can try to reduce the dose. Since Carbonel has been diabetic for a while, you may want to think about shaving a dose rather than a 0.25u reduction especially if your finding that dose reductions aren't holding.
Right now, what it looks like to me is that Carbonel may need more insulin. I would, however, encourage you to get at least one test per cycle when you can. It looks like you're not consistently getting PM tests. If it's feasible, can you always get a "before bed" test? The spot checks will help you to know if Carbonel's numbers are dropping lower in the middle parts of the cycle and then bouncing back up by shot time.
I'd also suggest evaluating the dose every 3 days/6 cycles. If Carbonel's numbers aren't where you want them, then consider increasing the dose. My concern is that if you hold a dose that is leaving your kitty in higher ranges for overly long, glucose toxicity can develop. What this means is that Carbonel's body gets used to being in higher numbers and treats that range as "normal." If this happens, it can make it harder to bring the numbers down. I'd also encourage you to think in terms of getting Carbonel to a dose that works. I wouldn't worry about the 0.75u being a good dose last summer. The only good dose is the dose that is currently working best for your cat.
ETA: Regarding syringe accuracy, there are several people here who use digital calipers to insure dose consistency. I'm going to ask Marje to stop by. I don't use calipers but she does and she can offer some input on the topic.