Hello and welcome!
I'm sorry your furry boy has you worried.
If his rear legs have appeared to be getting weaker over the years, it's possible he could have developed diabetes and a side effect of that is a neurological condition called diabetic neuropathy, which causes weakness in the hind legs.
There is another possibility for weak hind legs and that can be a blood clot lodged in the main artery carrying blood to the region. This is a symptom of a heart condition called cardiomyopathy.
In addition, if he's walking like he's drunk, this could be attributed to a vestibular disorder caused by an ear infection. The vestibular system controls balance/equilibrium and is typically started by an ear infection.
It's not uncommon for older cats to become constipated and that is because they usually do not drink enough. For the constipation, you can add 1 tsp. of plain canned pumpkin (not pie filling) to a small amount of his canned food twice daily, and then follow it with plain canned food. You can also water down his canned food and if he only eats dry food, this can be a cause, as well. Canned food is healthier for cats in general and the added moisture helps with constipation.
The higher than normal calcium level in his last blood test could have many causes. Ineffective function of the parathyroid gland, a parathyroid tumor, and kidney issues can contribute to a high calcium level, which can become a serious problem if not treated. Have your vet repeat the blood work to be sure your cat's calcium is above normal limits; if it is, then the cause must be identified so it can be treated. Here is more information:
I hope all will be well with your furry boy!
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