Stage 3 kidney disease in cats: what it means and how long cats live

What does stage 3 kidney disease mean?

If your cat has just been moved into stage 3, or diagnosed there, you've probably already seen the word "moderate" and searched for what it means for how long she has. I'll get to the numbers properly. But the first thing I'd want you to know is that stage 3 is where treatment does more for how a cat feels than at any other point in this disease.

In IRIS terms, stage 3 is moderate kidney disease. Enough working tissue has gone that the waste markers in her blood are clearly up, and this is usually the stage where cats start to feel it: weight loss, a patchy appetite, nausea, a duller coat. Some of that you may already have noticed and put down to her getting older.

Here's why that matters. Most of what makes a stage 3 cat feel unwell is a separate, treatable problem riding along with the kidney disease. Nausea is treatable. Dehydration is treatable. High phosphorus, low potassium, anemia: each has its own fix. The kidneys don't come back, but a cat whose passengers are being handled can feel a great deal better than her creatinine suggests.

The creatinine and SDMA range for stage 3

Before you take her stage as settled, check one thing: was she hydrated and otherwise well when it was measured? A cat staged on the day she came in dry and not eating can read a full stage worse than she is. If that's how she got her number, ask whether it's worth rechecking once she's stable. Sometimes a stage 3 on day one turns out to be a stage 2 cat who was dehydrated.

Substaging: protein and pressure

Urine protein, as a UPC. Under 0.2 is non-proteinuric, 0.2 to 0.4 borderline, above 0.4 proteinuric. Protein loss makes the disease progress faster, and in the study that measured it, cats above 0.4 had about four times the risk of dying during the study period. It's treated with a specific drug, usually telmisartan or benazepril, chosen and dosed against the number. If she's never had a UPC, this is the stage to get one.

Blood pressure. Under 140 is normal, 140 to 159 prehypertensive, 160 to 179 hypertensive, 180 and above severe. If your vet has the equipment, ask for a reading, especially at stage 3. If they don't, it's reasonable to ask whether a one-off visit somewhere that has a Doppler is worth arranging. Either way, sudden wide pupils or a cat bumping into furniture is an emergency visit now, because the window to save her sight is hours.

How long do cats live with stage 3 kidney disease?

About two years is the working median, and it's a rough guide rather than a forecast for her. In the largest survival study we have, 211 cats, the stage 3 cats lived a median of 778 days. The range in that same study ran from three weeks to almost six years, but that six-year figure is the single longest-lived cat, not something to count on. Most cats sat much closer to two years.

That range is the important part, more than the median. Two cats with the same stage 3 creatinine can be at opposite ends of it, and the difference usually isn't luck. It's whether the treatable things alongside the disease have been treated:

• Whether she keeps eating. The strongest single signal, and the one you can watch from your kitchen. A stage 3 cat who won't eat is usually nauseated rather than finished.
• Whether her phosphorus is on target. Above target, it damages what's left and makes her feel worse.
• Whether she's losing protein. About four times the risk above a UPC of 0.4.
• Whether high blood pressure, if she has it, is controlled.
• Whether anemia is caught and treated before it flattens her.
• What else she has, an overactive thyroid most often.
• How she responds over the first few months. In one study, cats whose disease held stable lived a median of 894 days, against 287 for cats whose disease kept progressing.

Two more things to hold onto. The study behind 778 days was published in 2008, before SDMA staging and before some of what we treat with now. And it's a median from one group of cats, so half of them did better. A stage 3 cat whose phosphorus is at target, whose nausea is handled, and who's eating is set up for the long side of that range.

The life expectancy page has the figures for every stage side by side, with the studies behind them.

What treatment looks like at stage 3

This is the stage where the treatment list gets longer, and where it pays off. Your vet will tailor it, but most stage 3 cats end up with some version of this.

Nausea control. This is the one I'd put first, because it's the one most often missed. A lot of kidney cats are quietly nauseated without ever vomiting: lip-licking, drooling a little, sitting over the bowl and walking away. An antiemetic like maropitant treats that. An appetite stimulant like mirtazapine makes her hungry and has only some anti-nausea effect, so a queasy cat needs the first one, not just the second. The nausea and vomiting page goes through it properly.

Appetite. If she's eating less, weigh her rather than judging by the bowl, and work through the causes in order. The appetite page is the one to read. Early on I push the kidney diet. By this stage, if she's eating something happily, her eating at all is starting to matter more than which can it came out of.

Phosphorus binders. If the diet alone doesn't get her phosphorus under 5.0, or she won't eat the diet, a phosphorus binder goes into her food. The dose is set against her bloodwork, not off a page.

Subcutaneous fluids. Often started at this stage, and it's the single most useful thing most owners learn to do at home. It doesn't treat the kidneys. It fixes the dehydration that damaged kidneys cause, which is a large part of why a kidney cat feels flat and won't eat. It looks impossible the first time and it's routine by about the fourth. The subcutaneous fluids page walks you through it.

Potassium, if her blood says so. Low potassium is common in the middle stages. It's decided on a blood value, and the potassium page explains why it needs rechecking as she goes.

Watch for anemia. Damaged kidneys stop sending the signal that tells the marrow to make red cells. If she's flat and tired, ask what her hematocrit is doing. IRIS says to treat when it's under 25 percent, or 25 to 28 if it stays there, and there are real treatments for it. The anemia page covers them.

Closer rechecks. Every two to three months is typical at stage 3, and sooner after anything new is started. The recheck page has the detail.

If her numbers jump suddenly, or she stops eating, get it worked up before anyone files it as the disease moving. Dehydration, a kidney infection with no outward signs, constipation, an uncontrolled blood pressure, a new drug, or a stone can each push a stable cat's numbers up, and several are fixable. The crisis days page covers how to tell, and the checklist there says what can't wait until morning.

What to ask your vet at stage 3

• Was she staged when she was well hydrated, or should we recheck now she's stable?
• What's our phosphorus target, and where is she against it?
• Do you think she's nauseated, even though she isn't vomiting?
• Should she be on subcutaneous fluids, and how much and how often?
• What's her UPC, and her potassium?
• What's her hematocrit, and what's the trend over her last few panels?
• Can her blood pressure be measured, here or somewhere else?
• How often do you want to see her, and what should make me phone sooner?

The view from stage 3

Stage 3 is the busiest stage for you. There are more tablets, maybe a fluids bag on the counter, more rechecks. It can feel like the disease has sped up, when a lot of what you're seeing is the treatment finally having something to work on.

The cats who do well here usually aren't the ones with the lowest numbers. They're the ones whose nausea got noticed, whose phosphorus got chased, and whose owners kept weighing them on Sundays. That's all in reach.

If she was diagnosed earlier than this, the stage 2 page covers the slower ground she came from. If her numbers move past 5.0, the stage 4 page covers what changes next, and it's worth knowing that even there, comfort is very much still treatable. The full chart for all four stages is on the IRIS stages page.