Stages of Kidney Disease in Dogs: Understanding the IRIS Guidelines

IRIS, the International Renal Interest Society, splits chronic kidney disease in dogs into four stages, based on creatinine and SDMA in the blood. Then it adds two substages that most owners never get told about: how much protein is leaking into the urine, and what the blood pressure is doing. A complete stage reads something like "Stage 2, proteinuric, hypertensive." All three parts matter, because the substages are what usually drive treatment.

If your dog has just been staged, you probably came here to find out what the number means. Here's the whole system, including the parts your discharge sheet may not have covered.

The four IRIS stages at a glance

IRIS is a non-profit, and the staging system it publishes is the one almost every vet in the world reaches for. The current version is the 2026 revision.¹

Staging is done after chronic kidney disease has already been diagnosed. It's done on a hydrated, stable dog, on fasting bloodwork, ideally measured on at least two separate occasions.¹ One bad result on a sick, dehydrated dog isn't a stage.

Those creatinine values assume an average size dog, and dogs at either extreme can sit outside them.¹ The SDMA numbers come from work using the IDEXX assay, so a different SDMA method may not line up.¹

If you're comparing your dog's bloodwork against a number you found somewhere else, check the units first. Ontario labs report creatinine in µmol/L. Most American sources quote mg/dL. They're the same measurement on different scales, and mixing them up is the single most common reason an owner thinks their dog is in a worse stage than they are.

What each stage means for your dog

Stage 1: kidney disease without azotemia

Creatinine is normal, or SDMA is normal to mildly up. The waste products haven't backed up yet.

So the diagnosis came from somewhere else: abnormal kidneys on palpation or imaging, protein in the urine coming from the kidney, an abnormal biopsy, or creatinine and SDMA that keep climbing on repeat samples even while staying inside the reference range.¹ A persistently high SDMA above 14 µg/dL can be used to diagnose early kidney disease on its own.¹

Dilute urine is where a lot of pet health articles go wrong. Without a non-kidney explanation it counts toward this diagnosis in cats, not in dogs.¹ Dogs concentrate their urine differently.

At Stage 1 I'm stopping any drug that's hard on kidneys where I can, ruling out treatable causes like a kidney infection or an obstruction, and measuring blood pressure and a urine protein to creatinine ratio.² That last pair is the substaging, and it's where the actual treatment decisions get made this early.

Stage 2: mild azotemia

At 125 to 250 µmol/L, most dogs still look completely well. Signs are mild, or there aren't any.

Here's what catches people out. The bottom of that range sits inside many labs' normal reference intervals. Creatinine is an insensitive screening test, so a dog near the top of "normal" often already has reduced kidney function.¹ That's the whole argument for running SDMA next to it.

This is the stage where I'd start talking about a clinical kidney diet, and IRIS makes the same point I would: it's much easier to switch a dog onto a renal diet now, before appetite starts to go.² A dog that already feels sick is a hard dog to convince about new food.

Phosphate control starts mattering here too. The target is a plasma phosphate under 1.5 mmol/L, and not below 0.9 mmol/L.² Diet first, then a phosphate binder if diet alone doesn't get there.

Stage 3: moderate azotemia, and the early/late split

Creatinine is 251 to 440 µmol/L. This is the widest stage in the system, and it's where dogs stop looking alike.

IRIS handles that by splitting Stage 3 into early and late. The split is not a creatinine cutoff. It's based on how the dog presents: no clinical signs points to early Stage 3, while many or marked systemic signs justifies calling it late Stage 3.¹

I mention this because owners often ask why their Stage 3 dog is bright and eating while a friend's Stage 3 dog is in hospital. Same stage, different half of it.

Treatment in early Stage 3 can look a lot like Stage 2, and that may be all a dog needs. As signs build, the emphasis shifts toward comfort: nausea and vomiting, appetite, anemia, dehydration and acidosis.² The realistic phosphate target loosens a little here too, to under 1.6 mmol/L.²

Stage 4: severe

Above 440 µmol/L. Most dogs here have several signs outside the kidney at once.²

Slowing progression still matters, but quality of life takes over as the priority. That means managing dehydration, acidosis, vomiting, nausea, poor appetite, weight loss and anemia.² Some of these dogs need fluids given routinely to hold their hydration.

The two substages most owners never hear about

The stage number leaves this out, and it's the part I most want owners to understand. IRIS substages every dog twice more: once on protein in the urine, once on blood pressure.¹

Owners come in able to tell me their dog's stage to the decimal, having never once heard the word proteinuria. The number they memorized is the least treatable part of the diagnosis.

Substage 1: protein in the urine

Measured as a urine protein to creatinine ratio, or UP/C. Urine dipsticks aren't reliable enough for this, so it needs the actual ratio run.¹

IRIS recommends running a UP/C on every dog with kidney disease, as long as there's no blood or inflammation in the urinary tract to muddy the result. Ideally it's based on at least two urine samples collected over two weeks or more.¹ A dog that keeps landing in the borderline band should be rechecked within two months.¹

Protein leaking through the kidney is both a sign of damage and a cause of more of it. Treating it is one of the few things that changes where a dog ends up. There's more detail in our guide to protein in the urine of dogs.

Substage 2: blood pressure

Substaging is done on systolic blood pressure, and it's graded by the risk of damage to other organs, meaning the eyes, brain, heart and kidneys themselves.¹

One reading doesn't substage a dog. The classification should rest on several measurements, preferably taken at different visits, or at minimum two hours apart in the same visit, with the dog given time to settle first.¹

The treatment goal is to get systolic pressure under 160 mmHg.² How fast we need to confirm the reading depends on how high it is: a dog in the 160 to 179 band gets confirmed over two to four weeks, a dog at 180 or above over one to two weeks. If there's already visible damage, such as bleeding or detachment in the retina, treatment starts without waiting.²

Treatment steps up in order. An ACE inhibitor such as benazepril first, then a higher dose, then adding a calcium channel blocker like amlodipine, then an angiotensin receptor blocker such as telmisartan if it's still not controlled.²

Put together, a full IRIS classification reads like this: Stage 2, borderline proteinuric, prehypertensive. If a dog is on treatment for blood pressure or proteinuria, the classification gets rewritten to reflect where they are now, with a note that they're being treated.¹

When creatinine and SDMA disagree

This happens more than you'd think, and IRIS has explicit rules for it. Creatinine drops as a dog loses muscle, so a thin, older dog can have a falsely reassuring creatinine. SDMA is less affected by muscle mass.¹

When SDMA says the disease is worse, IRIS says believe SDMA. In dogs:¹

The word doing the work there is "persistently." One discordant result gets repeated, not acted on.

SDMA isn't perfect either. Data is emerging on conditions that raise SDMA without any drop in kidney filtration, and lymphoma in dogs and cats is one of them.¹ Which is why I run both rather than picking a favourite.

How we diagnose kidney disease before we stage it

Staging only starts once the diagnosis is made, so it's worth knowing what makes the diagnosis.

For advanced disease it's straightforward: creatinine and SDMA are both up, plus urine that isn't concentrating properly, meaning a urine specific gravity under 1.030 in a dog.³

Early disease is harder, and takes one or more of: a persistent SDMA above 14 µg/dL, abnormal kidney imaging, or persistent kidney-origin protein in the urine with a UP/C above 0.5.³

The reason early detection is difficult at all is that the kidneys have a lot of spare capacity. Urine stops concentrating at around 66% nephron loss, and azotemia doesn't appear until roughly 75%.⁶ By the time creatinine moves, most of the damage is already done.

This is why I push senior bloodwork. Catching a dog at Stage 1 or early Stage 2 gives us room to act, and it's the whole point of senior pet care screening. Our in-house diagnostics run creatinine, SDMA, urine specific gravity and a UP/C from the same visit.

What the stage tells you about prognosis

These numbers aren't comforting. I'd rather give you the real ones.

Kidney disease in dogs isn't common. IRIS puts prevalence at 0.5 to 1.0%.⁷ A large UK study across 107,214 dogs in general practice found an apparent prevalence of 0.21%, with a true prevalence estimated at 0.37%.⁴ If you've read that a quarter of senior dogs have kidney disease, that figure doesn't hold up against the primary literature.

In that same UK study, median survival from diagnosis was 226 days, with a confidence interval of 112 to 326 days. IRIS stage at diagnosis and blood urea nitrogen were both associated with risk of death.⁴

Broken out by stage, reported median survival runs over 400 days for Stage 1, 200 to 400 days for Stage 2, 110 to 200 days for Stage 3, and 14 to 80 days for Stage 4.⁶

Read those two ways. They're medians, so half of dogs live longer, sometimes a lot longer. And the clock starts at diagnosis, which for plenty of dogs is already late.

Body condition turns out to matter a lot. In a study of 100 dogs with kidney disease, dogs who were underweight at diagnosis had a median survival of 25 days, against 190 days for dogs in moderate condition and 365 days for overweight dogs.⁵ Keeping weight on a kidney dog is not a cosmetic goal, which is part of why nutrition planning sits at the centre of management.

Dogs also do worse than cats with this disease, which surprises people who've had both. If you're comparing against a cat you've known, our guide to kidney disease in cats covers the feline side, and the staging cutoffs there are different.

Breed and size change the numbers

Greyhounds break the table, and it causes real misdiagnoses.

Healthy greyhounds run higher serum creatinine and higher SDMA than other breeds.¹ A retired racer with a mildly high creatinine may be entirely normal for a greyhound.

Sight hounds also tend to run higher blood pressure. IRIS recommends using breed-specific reference ranges where they exist, and grading risk by how far above that breed's range the dog sits rather than against the standard table.¹

Dogs at the extremes of body size can also fall outside the standard creatinine bands.¹ If you have a 4 kg dog or a 70 kg dog, the table is a starting point rather than a verdict.

What to ask at your next appointment

If you remember one thing here, make it this. Ask for all three parts of the stage.

Ask what the creatinine and SDMA were, and in which units. Ask whether a UP/C has been run, and what it was. Ask whether blood pressure has been measured, and how many times.

If the answer to either of the last two is no, that's a reasonable thing to ask for. Both are treatable, both affect how long a dog lives, and neither shows up in the stage number on its own.

I'd also ask what the recheck interval is and what would trigger an earlier visit. Kidney disease is managed on trends, not single results, and the trend is only as good as the schedule behind it.

If you're in Kitchener or Waterloo and want a second opinion on your dog's staging, call us at (519) 896-0532. Bring the bloodwork you have. Half the work is already done if someone's run the numbers.