IRIS stages 1 to 4, in plain English

What are the IRIS stages of kidney disease in cats?

Someone said "stage 3" to you, and then you got home and typed it into a search bar at eleven at night. That's usually how people arrive on this page.

So the first thing to say is what the stage is for. It's a shared description, so that any vet who opens her file knows roughly what they're dealing with, and so treatment decisions follow a consistent map instead of somebody's instinct.

It's a description of where she is right now. It's not a prediction and it's not a clock.

IRIS stands for the International Renal Interest Society, a group of veterinary kidney specialists who publish the staging system and the treatment targets that go with it. Your vet is following their guidelines, not making it up per patient, and that's a good thing.

The four stages

The stage is based mainly on creatinine, a waste product that healthy kidneys clear out of the blood. Here are the boundaries, in the mg/dL units most US labs report. If your lab reports in µmol/L, the numbers are in brackets.

Two useful things to notice. Stage 2 is a wide band, so a cat at 1.7 and a cat at 2.7 carry the same label and are not in the same situation. And crossing from 2.8 to 2.9 changes her stage on paper while changing almost nothing about her. The trend across several visits tells you far more than which side of a boundary she landed on.

Why the stage she was given might not be the right one

Staging is done on a well-hydrated, stable cat, ideally confirmed on two separate occasions. There's a real reason for that rule, and it matters to you.

A dehydrated cat's creatinine reads higher than her true kidney function. So a cat who was staged on the day she came in sick and dry can look a full stage worse than she is. After a few days of fluids the number often drops, and people quite reasonably think the treatment reversed something. It didn't. The first number was just flattering the wrong direction.

It runs the other way too. Creatinine comes from muscle, so a very thin cat who has lost a lot of muscle can have a deceptively low creatinine with poor kidneys behind it. That's one of the reasons SDMA is useful, because it doesn't depend on muscle mass in the same way.

If she was staged on her worst day, ask whether it's worth rechecking now that she's stable.

Stage, protein, pressure

Here's the part that gets left out, and it's the part I'd most want you to walk away with.

A stage on its own is an incomplete answer. IRIS asks for two more things alongside it, called substaging, and both of them are treatable problems that a blood panel won't show you.

Urine protein, measured as a UPC, the urine protein to creatinine ratio. It tells you whether her kidney filters are leaking protein. Under 0.2 is non-proteinuric, 0.2 to 0.4 is borderline, above 0.4 is proteinuric. It matters because protein loss makes the disease progress faster, and because there's a specific medication for it that your vet won't prescribe without the number.

Blood pressure. Under 140 is normal, 140 to 159 is prehypertensive, 160 to 179 is hypertensive, and 180 and above is severe. Somewhere between one in five and one in three kidney cats is hypertensive, and it usually causes no symptoms at all until it causes a permanent one, most often blindness from a detached retina. It's checked with a small cuff on a leg or the tail, it takes a few minutes, and it's treated with a daily tablet.

So the complete answer to "what stage is she" has three parts, not one. Stage, protein, pressure. If she has a stage but has never had a UPC or a blood pressure reading, that's a reasonable and specific thing to ask for at the next visit.

What changes at each stage

Broadly, and your vet will tailor it:

Stage 1 and 2. Mostly monitoring and phosphorus. Treat the protein loss if there is any, treat the blood pressure if it's high, get her onto a lower-phosphorus diet if she'll take it. The temptation here is to over-treat a cat who feels perfectly well, and there's no need.

Stage 3. This is where the work is, and where most of what's on this site becomes relevant. Phosphorus binders, subcutaneous fluids, antiemetics, potassium supplementation, watching for anemia, rechecks closer together.

Stage 4. Symptom control moves to the front. Fluids, nausea control, appetite, anemia treatment, comfort. One thing worth knowing specifically: potassium flips direction in late stage 4. A supplement that was right for her in stage 2 can become dangerous when she's barely producing urine, which is why potassium is decided on a blood value and never on last year's prescription.

The other thing the stage sets is her phosphorus target, and those targets are tighter than the plain reference range on your lab sheet for cats in the later stages. Ask your vet what number they're aiming for in her specifically, rather than whether it's technically inside the printed range.

Does the stage tell me how long she has?

Not on its own, and I'd rather give you the honest version than a comfortable one.

The published medians run to roughly three years from diagnosis for stage 2, somewhere around two years for stage 3, and months rather than years for stage 4. Those are medians from studies that are getting old now, drawn from cats who were treated with less than we have available today, and the spread around each of those numbers is enormous. Individual cats sit a long way either side.

What predicts her course better than the stage does: whether she's eating, whether she's losing protein in her urine, and whether the treatable things alongside the kidney disease have actually been treated. Most cats are diagnosed at stage 2, and stage 2 cats commonly go on for years.

There's more on this, including how to think about the numbers without letting them run your week, on the life expectancy page.

What to do with the number you were given

Write it down with the date, along with her phosphorus, her potassium and her weight. Ask what her UPC and her blood pressure were, and if the answer is that they weren't done, ask for them at the next visit.

Then put it away. The stage is a tool for deciding treatment, and it does that job well. It's a poor tool for predicting the future, and it's a terrible one to sit and stare at.

If you want the values themselves explained one at a time, that's the bloodwork page.