Your cat has kidney disease. Start here.

Find the printout your vet gave you. It looks something like this one:

These are the ones that matter:

The UPC is the one to ask for by name. It's cheap, it needs no special equipment, and it changes what she's prescribed. If she has a stage but has never had one, that's a fair thing to raise.

If a number on your sheet isn't in that list, it's on the full page, along with what a high one and a low one each mean.

Vets stage kidney disease from 1 to 4 using a system called IRIS, a scale published by an international group of kidney specialists. It's based mainly on creatinine, measured when your cat is properly hydrated.

Ask your vet which stage she's in and write it down. Everything else on this site is easier to apply once you know it. A stage describes where she is now. It does not predict how long she has: for that question, asked honestly, see life expectancy by stage.

If you have the whole sheet, put the numbers in and I will read creatinine, SDMA and phosphorus together.

Almost every owner's first instinct is to fix the eating. It's the wrong order. A cat who's nauseated will refuse whatever you offer her, and worse, she'll learn to associate that food with feeling sick, so you burn through her favorites one at a time.

Cats are quiet about nausea. Most don't vomit. They sit hunched in front of a full bowl, lick their lips, turn their head away, and walk off. If that's what you're seeing, ask your vet about an anti-nausea medication before you buy another flavor of food.

Two other things look exactly like kidney nausea and need completely different treatment. Constipation, because a mildly dehydrated cat's stool dries out, and a constipated cat is nauseated, flat and often in and out of the litter box straining. And a painful mouth, where the tell is that she's clearly interested, comes to the bowl, then flinches away or chews on one side. No anti-nausea drug fixes a sore tooth. Both are on the nausea page.

Damaged kidneys can't concentrate urine, so your cat loses more water than she should and spends most of her time mildly dehydrated. That's a large part of why she seems tired.

Start with the easy things: wet food instead of dry where she will accept it, more water bowls in more rooms, a wide shallow bowl rather than a deep narrow one, and a running fountain if she likes moving water.

If your vet has recommended subcutaneous fluids, sterile fluid run under the loose skin between her shoulder blades, which her body absorbs over a few hours, it is the single most useful thing most owners learn to do at home, and not a sign that things are dire. It looks impossible the first time and it's routine by the fourth.

There's an order to this, and knowing it stops you chasing the perfect bowl.

If she won't take the kidney diet, don't force it. Transition slowly, mixing a little of the new food into the old over a couple of weeks. If she still refuses, tell your vet. A phosphorus binder, a powder mixed into whatever she will eat that traps phosphorus in the gut, gets you a good part of the same benefit.

A cat eating an ordinary food beats a cat refusing the correct one.

Put the medications on the fridge with the times you actually give them, not the times you intend to. Buy a cheap kitchen scale and weigh her once a week, same day, and write it down. Weight is the most useful thing you can track at home.

Note what she eats, roughly. Note the litter box. You're building the ability to answer "is she better or worse than last month" with something other than a guess, which is a different job from keeping a medical record.

Newly diagnosed cats usually need rechecking in two to four weeks, sooner than most people expect, because the first set of numbers was taken on a bad day and we need to know where she settles.

That interval isn't one number for everybody, so ask for hers specifically. A stable early-stage cat may well be fine months out. A stage 4 cat, or any cat who has just been started on fluids, a blood pressure drug or an ACE inhibitor, usually needs to be seen inside a week or two.

On blood pressure, I'll be straight with you. High pressure does hide alongside kidney disease, and its first symptom is often sudden, permanent blindness, so it's worth measuring where it can be measured. But the machine is expensive and the reading is genuinely difficult to get right in a cat. I don't have one, plenty of clinics don't, and those cats are still managed well. What I'd want you doing instead is watching her eyes, and calling the same day if her sight changes. There's more on the blood pressure page.

One more to know about, because it's easy to miss. If her numbers have got worse without an obvious reason, ask about a urine culture collected by cystocentesis, a sample taken with a needle straight from the bladder. A silent kidney infection is one of the more common causes of a cat who suddenly got worse, and it's curable.