Stage 4 kidney disease in cats: what it means and how long cats live

What does stage 4 kidney disease mean?

If you've just heard the words "stage 4," you may be reading this in a parked car or late at night, and you probably came here for one number. I'll give it to you honestly in a moment. First, two things I'd want you to know before you read it.

Stage 4 is the most advanced of the four IRIS stages. The kidneys have lost most of their working tissue, the waste markers in her blood are high, and the signs are usually obvious by now. From here the focus moves toward how she feels, day to day, rather than how the disease behaves on paper.

And that focus is not a small thing. Comfort is very much still treatable at stage 4: hydration, nausea, appetite, anemia, warmth. A lot of what makes a stage 4 cat feel terrible is a separate problem sitting on top of the kidney disease, and separate problems can be fixed.

The creatinine and SDMA range for stage 4

The single most useful question to ask about that number: was she dehydrated, or sick with something else, when it was drawn? Plenty of cats get their first stage 4 result on the day they come in at their worst. A dry cat's creatinine reads higher than her true kidney function, and a few days of fluids can bring it down a long way. That doesn't mean the kidneys healed. It means the first number was measured on her worst day, and her real starting point is the one worth planning around.

Substaging still matters

Urine protein, as a UPC. Under 0.2 is non-proteinuric, 0.2 to 0.4 borderline, above 0.4 proteinuric. Blood pressure. Under 140 is normal, 140 to 159 prehypertensive, 160 to 179 hypertensive, 180 and above severe. If your vet can measure it, ask for a reading at this stage. Sudden blindness, with pupils that go wide and stay wide, is still an emergency visit now at stage 4, because it can sometimes be saved if it's caught within hours.

How long do cats live with stage 4 kidney disease?

Usually months rather than years. In the largest survival study we have, 211 cats, the stage 4 cats lived a median of 103 days, about three months. A very few cats in that study lived for years, one past five, but those were rare exceptions.

I know that median is hard to read. Here's what I'd hold alongside it.

• It's a median. Half the cats did better than three months, and half did worse. The cats who lived for years were rare, and I wouldn't plan around being one of them.
• It's from 2008. That's before SDMA staging and before some of what we treat with now.
• It starts the clock at the stage 4 result. If that result came from a dehydrated cat in crisis, she may not truly be where the number put her.

The life expectancy page has every stage side by side with the studies behind them. But at stage 4 the more useful number is the one she gives you over the next few weeks. A cat who's eating, holding her weight, and steady at her next recheck has already told you more than the study can.

Is it the end, or a bad week?

This is the most important practical thing on this page. A stage 4 cat who crashes is very often dealing with something on top of her kidney disease, and a lot of those things are treatable:

• dehydration, which is the most common
• a kidney infection with no outward signs, found with a urine culture collected by needle straight from the bladder
• constipation, which is common in kidney cats and badly under-recognized
• high blood pressure that hasn't been found, or isn't controlled
• a new medication, especially any anti-inflammatory meant for a person
• potassium that's gone the wrong way

A cat with one of those can feel considerably better in a few days. That's worth finding out before anybody concludes anything. The crisis days page covers how a vet tells a detour from the disease moving, and the checklist there is what means a call tonight rather than in the morning.

What treatment looks like at stage 4

The aim changes here. It's less about slowing the kidneys and more about making each day a good one for her.

Fluids. Hydration is the foundation of how a stage 4 cat feels. If she isn't on subcutaneous fluids already, ask about them. If she is, ask whether the amount still fits, and don't change it yourself, because too much fluid is a real risk in a cat with heart disease or high blood pressure.

Nausea and appetite. Treat the nausea first, then help the appetite if she still needs it. Many nauseated kidney cats never vomit. They lick their lips, walk up to the bowl and walk away, or eat two bites and leave. The nausea page and the appetite page cover what to ask for.

Food. Early on I push the kidney diet, because it buys real time. By stage 4, her eating at all matters more than the brand on the can. If she's happy eating something, I'm not going to spend her good days arguing with her about food, and I'd rather you didn't either.

Anemia. Common at this stage and very treatable. If she's flat and tired, ask what her hematocrit is doing and whether darbepoetin or molidustat is an option. Many cats are noticeably brighter once it works. The anemia page explains it.

Potassium, carefully. This is the one I'd most want you to know. Earlier in the disease, kidney cats lose potassium and often need a supplement. Late in stage 4, when she's producing little urine, potassium can build up instead, and high potassium affects the heart. A dose that was exactly right at stage 2 can be harmful now. It's decided on a blood value, never on last year's bottle. The potassium page has the detail.

Rechecks. Every two to four weeks, sometimes closer. Things move faster and the margins are thinner.

Her mouth and her joints. A sore mouth from uremic ulcers, and arthritis that's been put down to old age, are both worth raising by name. Neither is the kidney disease itself, and both can be treated. For pain I use buprenorphine, and gabapentin at a reduced dose because the kidneys clear it. I never use an NSAID in a kidney cat, and I don't use Solensia, the monthly arthritis shot, in one either. The life expectancy page explains why.

A note on feeding tubes, because you may hear about one. If she keeps eating too little despite nausea control and an appetite stimulant, a feeding tube is an option some hospitals offer. I don't place them myself because of the anesthetic, and the appetite page covers what one involves and when it's worth discussing.

What to ask your vet at stage 4

• Was she dehydrated or sick with something else when this number was drawn, and should we recheck once she's stable?
• Could anything treatable be sitting on top of this: an infection, constipation, her blood pressure, a medication?
• Is she nauseated, and is she on something for it?
• Are her fluids at the right amount for her now?
• What's her potassium, and does her supplement still make sense?
• What's her hematocrit doing?
• Is her mouth sore? Could she have arthritis?
• How often do you want to see her, and what should make me phone tonight rather than wait?

Where the hard part is

At some point, for most stage 4 cats, treatment stops buying good days and starts buying days. Those aren't the same thing, and telling them apart is the hardest judgment in this whole disease. It usually isn't a lab number that tells you. It's the day she stops doing the two or three things that make her who she is.

I've written about how I think about that, including a simple test built around the three things your cat loves most, on knowing when it's time. Reading it early, while there's nothing to decide, makes it easier rather than harder, and I'd say that whether she has weeks ahead of her or years.

For today, though, if she's eating something and still interested in her own life, the median isn't the thing to be watching. Her weight on Sunday is, and how she does at her next recheck.

If you're looking at an earlier result, the stage 3 page covers the ground before this one. The full chart for all four stages is on the IRIS stages page.