Cats may show symptoms like extreme thirst and hunger, litter box problems (ie. urinating outside the box), skin problems, and behavioral changes. Unfortunately it can be particularly difficult for people with multi-cat households to notice changes in one cat.
However, if you do suspect that your cat may be showing symptoms, separate the cats and give each their own food & water bowls, as well as a litter box. The cats should be confined in areas completely separate from one another for a few days so that you know which cat is behaving in what way.
A trip to the vet for a blood test will allow your vet to diagnose whether your cat has diabetes (or any other disease). The amount of glucose in your cat's blood will be measured. High blood sugar suggests diabetes, however, your vet may decide to repeat the test to confirm the diagnosis. Sometimes cats develop transient diabetes (also called transient hyperglycemia), or a temporary period of high blood sugar. This can be caused by changes in your cat's routine or home (which can cause cats to be stressed), or from medication.
Some cats will require insulin shots. Others may be able to get by with a change in diet and oral medications. Your veterinarian will determine how high (and how consistently high) your cat's blood glucose levels are, to recommend whether or not insulin shots should be given. Your vet can show you how to administer these shots to your cat.
When it comes to diet, diabetic cats need to be fed on a regular schedule to keep blood sugar levels under control. But pet owners need to monitor the portions fed to ensure the cat doesn't gain weight. Your vet may recommend that you split the cat's daily amount of food into two or three separate "mini-meals".
Every cat is an individual and there may be a period of adjustment until you and your vet can find the right treatment for your feline friend. The purpose of insulin is to lower blood sugar, so knowledge of the signs of hypoglycemia in cats is essential.
Cats can be unpredictable creatures. Even if you feed your cat on a regular schedule, with the same amount of food, and give the exact dosage of insulin as scheduled, your cat may still become hypoglycemic. This can be caused by the cat eating less than usual (or not eating at all), or vomiting up the food.
Of course, it's also important to make sure the insulin dosage is correct and it's given on schedule. You may want to put up a "checklist" for your family - whomever gives the cat its insulin initials a box next to that scheduled dosage. This can help families to avoid "double-dosing" the cat. Too much insulin can lead to hypoglycemic shock, which can become life-threatening. If you notice your cat showing signs of hypoglycemia, rub Karo syrup or corn syrup on its gums. Once he starts to respond, call your vet and bring him in immediately for assessment.
If you're not sure whether someone else has already given the cat its insulin dose, it's better to hold off on giving the shot and call the vet for advice.
Always be watchful for changes in your cat's behavior. Even if your cat appears to be doing well on his diabetes treatment plan, sometimes a cat's body will start reacting differently and the insulin dosage may need to be changed.
Finally, it's a good idea to keep your cat indoors. Diabetes in cats must be managed and an indoor cat is much easier to monitor. Toys, family interaction, window perches, and other such things can help to keep your cat stimulated and happy.