Diabetes is usually a disease of fat cats. It is similar to adult onset in humans. Is/was your cat overweight?
There are several other common causes of increased urination and drinking in older cats. at the top of the list is kidney disease. Hyperthyroidism is the other major player that increases water intake and output. Liver disease, some types of cancer, infections, are other possible causes.
Blood tests can differentiate between most of the causes (diabetes, kidney disease, hyperthyroid, liver disease and sometimes infection).
Mot of these can be treated with reasonable success although usually not cured.
Let me know if you have follow up.
Enjoy your baby girl!
You are a diabetic and I'm guessing that you have a home glucose meter. Most of my clients with diabetic cats do routine testing at home, but I can teach them techniques face to face. They use the little vein that runs on the outer edge of the mid thin part or the ear. Alcohol helps visualize it. A quick cross scratch is the easiest way to nick it, but the lance that come with the kits can be used directly over the vein also. Once a drop of blood is there, the test is easy particularly for someone who already knows how to use the meter.
Be very careful that you and your wife are not hurt. It is not worth, and will not do your cats any good, if you get an infection from a cat scratch or bite.
Urine, as you know, is not as good an indicator of blood glucose, but it is good enough to determine if a cat is diabetic. You can get urine by putting plastic wrap on top of kitty litter in the box and testing urine there. You need to watch carefully because the cats will scratch the plastic after urinating. Some cats will use an empty box.
I would not be surprised if you cat does not have diabetes. Diabetic cats often become insulin sensitive and normoglycemic when they lose weight.
A chemistry screen, blood count and thyroid function will require a vet. Your house call person can do that perhaps on a routine call sometime.
The mainstay of treatment for kidney failure is decreasing protein. Senior and weight loss diets have decreased protein, but you need to read the label and factor in water content to really compare them.
Hyperthyroid cats are usually hyperactive and nervous. This is a change in behavior not just what is normal for an individual. cat Heart rate increases to over 200 beats per minute. Normal is around 160-180. The pulse can be felt along the thigh bone of the inside of a back leg or over the heart. If you have a cat friendly home nurse, you might be able to convince her/him to check the heart rate.
Most importantly, recognize that 15 is a very respectable age for a cat. Do what you can, and it sounds like you are, to keep her comfortable. She needs as much water as she will drink, good food and lots of love. Most of us would be happy if we got that out of life.
I hope some of this helps and follow up questions are welcome.
Veterinarian
30 years as owner of a mobile practice treating dogs, cats, horses and other pets.