Chronic kidney disease is the most common serious diagnosis in older cats. Up to 40% of cats over the age of 10 have it. By the age of 15, that figure climbs to around 80%.
Most of them show no symptoms until the disease is already well advanced, because cats compensate silently while their kidney function quietly declines.
What CKD actually is and how it gets diagnosed
The kidneys filter waste products from the blood and regulate fluid balance. In CKD, kidney tissue progressively scars and loses function .. and unlike some organs, kidneys can't regenerate. Once that tissue is gone, it's gone.
What makes CKD particularly brutal is that the damage becomes self-perpetuating. When nephrons .. the kidney's functional filtering units .. are lost, the remaining ones work harder to compensate.
That increased workload causes scarring in those nephrons too. As filtration declines, phosphorus accumulates in the blood, which accelerates fibrosis and causes soft tissue mineralisation. The kidneys also become increasingly oxygen-starved as blood flow deteriorates, which triggers oxidative damage and more scarring.
Meanwhile the damaged glomeruli start leaking protein into the urine, and those filtered proteins cause further inflammation in the surrounding tissue. Each mechanism feeds the others. It's a cycle that, once established, the body cannot break on its own.
Two things follow from this. The first is anaemia. Healthy kidneys produce erythropoietin, the hormone that signals the bone marrow to make red blood cells. Failing kidneys produce less of it.
The resulting anaemia means less oxygen reaches the remaining kidney tissue, which accelerates the damage further. The second is hypertension. The kidneys regulate blood pressure, and as they fail, blood pressure rises. Sustained high blood pressure then causes additional kidney injury. Again, a cycle.
On top of all of this, waste products that would normally be filtered out accumulate in the blood .. not just creatinine and urea, but compounds like indoxyl sulfate and p-cresyl sulfate, produced by gut bacteria from dietary protein.
These uremic toxins directly promote tubular inflammation and drive further kidney injury, and they also cause the nausea, appetite loss and lethargy that make CKD cats feel so unwell in later stages.
In plain language: the kidneys break down, the body tries to compensate, and in doing so breaks them down faster. The cat feels nothing until the damage is already severe. By the time you notice something is wrong, a lot has already been lost.
What it actually looks like
In the early stages, usually nothing obvious. Maybe a little more water consumption than usual. A slightly thinner frame. A coat that's lost some of its condition. Things that are easy to write off as ageing.
As the disease progresses, appetite drops, the cat becomes lethargic and withdrawn, vomiting becomes more frequent, and the breath takes on a distinctive unpleasant smell from the waste compounds building up in the blood.
Mouth ulcers can develop for the same reason. In late stages the cat may stop eating almost entirely, become severely anaemic .. visibly pale gums, extreme weakness .. and deteriorate quickly.
The cruelest part is that by the time the obvious signs appear, around two thirds of kidney function is already gone. The early window, when intervention has the most impact, is almost always silent.
Diagnosis is made through blood markers. The traditional one is creatinine, though it has limitations .. it only rises noticeably once a significant proportion of kidney function is already lost. A newer marker, SDMA, is more sensitive and can detect decline earlier. From there, vets use the IRIS staging system to classify severity from Stage 1 (early, often no symptoms) through to Stage 4 (severe).
Cats are also assessed for proteinuria and blood pressure, which affect prognosis and management. The majority of cats are diagnosed at Stage 1 or 2, where the disease is present but the cat may appear completely normal.
Given how silent early CKD is, most vets recommend annual bloodwork and urinalysis starting around age 7, moving to twice-yearly screening from around age 10 onward. Since the disease can be well underway before any symptoms show, this is one of the few places where catching it early genuinely changes what your options look like.
One thing worth knowing if your cat is raw fed: creatinine levels can run slightly higher in raw fed cats due to higher dietary meat content, and this can be misread as early kidney disease. It's worth flagging your cat's diet to your vet before bloodwork is interpreted.
What you will almost certainly be told to feed
The standard recommendation is a prescription renal diet. These are low in phosphorus, low in sodium .. and low in protein. Some vets will suggest the wet version over dry, and yes, the moisture content is better. But the protein content and quality is no different. You are still feeding a heavily processed, low protein formulation .. just with water added.
The phosphorus restriction has solid reasoning behind it: phosphorus accelerates kidney damage, and managing it slows disease progression. That part isn't controversial.
The protein restriction is a different conversation. Cats are obligate carnivores. Their metabolism is built around protein .. they can't downregulate protein metabolism the way other animals can. When dietary protein is insufficient, the body doesn't simply adjust. It starts breaking down lean muscle mass to meet its own needs. This isn't a theory. It's documented. And yet the standard prescription renal diet asks cats with already compromised health to eat less of the one macronutrient their physiology is most dependent on.
What the research says .. and what's still unresolved
Current evidence on protein restriction in CKD cats is genuinely divided. Some research supports moderate restriction to reduce uremic toxin buildup. Other research suggests that over-restriction accelerates muscle loss without clear benefit to kidney function, and that the priority should be high-quality, highly digestible animal protein rather than simply less protein. This is an active debate within veterinary nutrition. It isn't settled.
It's also worth asking why long-term, prospective dietary studies in CKD cats are so rare, and who funds the research that does exist. I'll leave that as a question rather than a statement.
There are a few things worth raising with your vet if your cat is diagnosed. Phosphorus management is well established and not controversial. Moisture intake is worth asking about too, particularly if a dry prescription formulation is being suggested for a cat whose kidneys are already under strain. And it's reasonable to ask not just how much protein a diet contains, but what quality and digestibility that protein is.
None of this is a substitute for your vet's assessment of your individual cat .. IRIS stage, bloodwork and clinical signs all matter for what's appropriate. But they're reasonable questions to bring into that conversation.
What I've noticed
I've spent almost ten years watching cats with CKD on a low phosphorus, high moisture raw diet, alongside owners navigating that diagnosis. It's given me plenty of reason to keep coming back to the same questions .. about phosphorus, about moisture, about protein quality versus protein quantity.
I don't have controlled data, and I'm not going to pretend otherwise. What I have is nearly a decade of watching this play out, and a real curiosity about why these questions don't get asked more often.
On raw feeding specifically
If you're already raw feeding, or considering it, phosphorus and moisture are two things worth understanding whatever you end up feeding. Phosphorus can be managed through ingredient selection, and a fresh diet is naturally higher in moisture than a dry one. What's right for your cat still depends on their individual bloodwork and your vet's assessment, but these are useful concepts to have in your back pocket when that conversation happens.
We've helped a lot of owners navigate the diet question after a CKD diagnosis, so if you're going through one with your own cat, feel free to reach out. We're happy to talk about raw feeding in relation to low phosphorus requirements.