Her Creatinine Dropped at the Last Recheck. Why CKD Cats' Creatinine Goes Up, Then Down, Then Goes Up Again. 

Renal diet, sub-Q fluids at the kitchen table, a phosphate binder in every meal — the full CKD protocol, and the number still bounces at every recheck. After twelve years in feline consults, here's the one thing I watched the creatinine chart never tell a CKD owner.

Updated 15 Sep 2026

Read time: 5 mins

Written by Kayla Brooks

RVN Registered Veterinary Nurse, feline medicine

If your cat has been on the expensive renal food for months and the creatinine is still creeping.

 

If sub-Q fluids brought the number down for one recheck and it was back up by the next.

 

If she's drinking more, eating less, and somehow the bloods came back "stable."

 

If you've stopped celebrating a good result because you've learned what usually follows it.

 

Then this is for you, and I'm going to be blunt about something I watched happen in hundreds of consults.

The Conversation I Sat Through More Than Any Other

I spent twelve years nursing in small-animal practice, most of it in a clinic with a heavy feline caseload. CKD cats were our regulars. I knew their names, their owners' cars, which one would wee in the carrier before we'd even drawn blood.

 

The protocol was almost always the same three things:

 

A prescription renal diet. Subcutaneous fluids at home if she was drying out. A phosphate binder mixed into the food.

 

And the pattern was almost always the same too. The creatinine would come down. The owner would exhale. Three months later — same carrier, same vet, same number back up, or higher.

 

Nobody was doing anything wrong. Every one of those three things is a reasonable tool. But I want you to notice what each one actually does, because it explains why the number keeps bouncing.

Why the Number Bounces — and Why That's the Clue, Not the Result

A CKD kidney isn't one problem. Veterinary literature describes feline chronic kidney disease as an interaction between three things: the inflammation and scarring happening inside the kidney tissue itself, the waste load arriving at what's left of it, and the muscle her body is quietly burning to stay alive.

Line the standard protocol up against those three:

 

Renal diet — cuts phosphorus and protein waste. Turns the volume down on the workload. Does nothing to the inflammation in the tissue, and the lower protein quietly speeds up the muscle loss.

 

Sub-Q fluids — rehydrate her. Dilute the blood, flush the waste, and the number drops for the recheck. Powerful, and often necessary. Also does nothing to the inflammation, and the effect is gone in days.

 

Phosphate binder — catches phosphorus in the bowl. Doesn't touch inflammation. Doesn't touch muscle.

 

Each one pulls the workload lever, harder or softer. None of them pulls the other two. So the number moves with whichever lever was pulled most recently — mostly hydration — and drifts back the moment that lever eases.

 

That's the cycle. The number goes up and down. The kidney only goes one way.

 

And the cruellest part is that a falling number isn't always the kidney improving.

 

Because inflammation — the first lever — is the one almost nobody is deliberately treating between rechecks. And I'll come back to why "down" can be the worst result on the page.

What "Stable" Actually Means in a Cat's Kidney

I'm going to say the thing vets say carefully, because you deserve to hear it plainly.

 

Creatinine doesn't rise until roughly three-quarters of her kidney function is already gone. By the time there's a diagnosis, the tissue has been under low-grade inflammation for years. Nephrons don't regrow. What replaces them is scar, and scar doesn't filter anything.

 

I'm not telling you she's dying. I'm telling you that "stable on the recheck" is a snapshot of how hydrated she was that morning, not of what her kidney tissue did in the ninety days since. Every month the inflammation runs unopposed is a month more nephrons are being replaced with scar — and that loss never shows up as a bounce. It only shows up as the floor moving.

 

The goal isn't just a good number. It's a kidney that's being actively managed on the days that look fine.

The Second Problem Almost Nobody Is Treating

Here's the research that changed how I think about these cats.

 

A 2019 study compared cats with chronic kidney disease against healthy cats and measured a toxin called indoxyl sulfate in their blood — a compound the kidney is supposed to clear, but that the kidney does not make.

 

It's made by gut bacteria, from the protein in her food.

 

CKD cats carried significantly higher levels of it, and the level climbed with each IRIS stage. Their gut bacterial diversity was lower, too.

 

In plain language: part of what's poisoning her kidney isn't coming from her kidney. It's being manufactured in her gut, every day, from every meal. A phosphate binder can't touch it, because it isn't phosphorus. A renal diet lowers the supply, but doesn't change which bacteria are doing the manufacturing.

 

And you can't fix it by just adding a probiotic, because the bacteria you add have nothing to live on in a gut that's been starved of fibre and fed a restricted diet for a year.

The Three Things the Renal Literature Keeps Coming Back To

1. Marine omega-3s — EPA and DHA.

 

The landmark study here followed 175 cats with CKD across seven different commercial diets. Cats eating a renal diet survived a median of 16 months, against 7 months on ordinary food. And the single diet associated with the longest survival — 23 months — was the one with the highest EPA content.

 

A separate veterinary review discusses EPA and DHA as a way to help modulate inflammatory responses, and gives empirical feline intake ranges:

  • EPA: 17–25mg per kg of bodyweight, per day
  • DHA: 8–18mg per kg, per day

For a typical 4kg cat, that's roughly 68–100mg of EPA per day. Remember that number — most "cat fish oil" doesn't tell you what a dose actually delivers, and most owners have never done the maths on their bottle.

 

For a CKD cat, this isn't about a shinier coat. It's about inflammatory balance inside the tissue that's being scarred.

 

2. A synbiotic — probiotic plus prebiotic, together.

When gut bacteria have fermentable fibre to eat, they ferment fibre. When they don't, they ferment protein — and protein fermentation is where indoxyl sulfate comes from. Give the bacteria a prebiotic to live on and the chemistry shifts: less toxin built, more of it trapped and passed in the stool instead of absorbed into the blood the kidney has to clean.

 

That's a lever the kidney never has to pull. The gut pulls it for her.

 

3. The muscle — the thing the number is actually made of.

 

This is the lever nobody names, so I'll name it.

 

Creatinine is a waste product of muscle. Not of the kidney — of muscle. A cat with more lean mass makes more of it; a cat wasting away makes less. So when a CKD cat loses muscle over her spine and hips, her creatinine can read lower at the next recheck while her kidney is doing worse.

 

That's why a 2014 study found a newer marker, SDMA, rose an average of 17 months before creatinine in cats with CKD — because SDMA isn't tied to muscle, and creatinine is.

 

The "good" result that came down after she'd got thinner? That's the number lying to you. And the muscle she burned to make it lie is muscle she may not get back.

 

So the real question isn't "should I add fish oil?" It's:

 

Can I support inflammation, the toxin load and her muscle every single day — without adding three more products to a routine that's already breaking you?

Why This Was Nearly Impossible in Practice

Because I tried. I recommended it. And I watched it fail for reasons that had nothing to do with the science.

 

She wouldn't eat it. A CKD cat is already nauseous, already off her food, already suspicious of the renal diet you fought to get her onto. You add a strong-smelling fish oil. She sniffs and walks away, and now you've cost her a meal — and CKD cats can't afford to skip meals.

 

The bottle changed on the counter. EPA and DHA oxidise. Every pump lets in oxygen and light. By week three the oil smells different, and a cat with a uraemic stomach notices before you do.

 

It broke the renal diet. Most fish oils and gut supplements don't publish their phosphorus. Some carry salt, flavourings, or protein of unknown origin. Owners who'd worked for months to get phosphorus down — rightly — wouldn't risk it.

 

It was three products. Fish oil, probiotic, prebiotic. Three costs, three doses, three chances for her to refuse one and the whole routine falls over.

 

For most of my career, the honest advice was: "the evidence is good, but I don't know a way to actually get all of it into your cat."

 

Then I found the one product that fixed all four.

What Fureeze Built — and Why It's Different

Fureeze is an Australian company (they ship to the US and UK too) whose founder ran into the same four walls I did. He couldn't find a fish oil that was still fresh on day 28, that a sick cat would reliably eat, that didn't quietly undo a renal diet, or that didn't turn one supplement into three. So they stopped selling bottles altogether.

 

Every serving is sealed in its own snap-pack. Snap, squeeze over food, done. No pump, no measuring, no fridge. Each pack stays airtight — with vitamin E as a further guard — until the moment it hits the bowl. Oxygen and light never touch the oil, so day 28 smells exactly like day 1. For a cat who walks away from anything that smells off, that's the whole game.

 

Then they published the numbers most brands hide, and built all three levers into the one pack:

 

Inflammation

  • 160mg EPA, 118mg DHA — 278mg combined per snap-pack
  • Antarctic krill oil, 100mg — omega-3 carried on phospholipids, which the body takes up through a different route from standard triglyceride fish oil

 

Toxin load

  • Lactobacillus plantarum, 100 million CFU — a live probiotic for the depleted gut the 2019 study measured
  • Mannan oligosaccharides (MOS) — the prebiotic half, so those bacteria ferment fibre instead of protein. Probiotic plus prebiotic is a synbiotic — the lever the kidney never has to pull

 

Muscle

  • Taurine, 120mg — the amino acid a cat on a protein-restricted diet is most often short on
  • The same EPA and DHA that inflammatory muscle loss runs on, delivered fresh every day instead of oxidised

Plus astaxanthin 2mg and vitamin E — antioxidant support for tissue under oxidative stress — with negligible phosphorus and no added salt.

 

On the dose. Remember the range for a 4kg cat: 68–100mg EPA a day. One snap-pack is 160mg — a full daily dose for a 6–8kg cat. For a smaller or more nauseous cat, start with half a pack for the first week and move to a full one once she's eating it cleanly. You can't do that with a pump. You can with a pack you squeeze.

 

Inflammation. Toxin load. Muscle. One snap-pack.

 

Here's how it works:

"But She's on a Strict Renal Diet"

This is the question I'd want answered before anything else, so here it is on its own.

 

A snap-pack is oil, not a meal. It adds negligible phosphorus (only 1.2mg), no salt, and its only protein is hydrolysed chicken — broken into fragments so small the gut barely registers them as protein. The phosphorus you fought to get down stays down.

 

This is the first product I've been able to point to and say: the phosphorus is accounted for, the protein source is on the label, and it was designed with the renal-diet cat in mind.

Will She Actually Eat It?

Everything above is worthless if it fails the only test that matters in a CKD household.

 

Fureeze ran an in-house double-blind palatability trial across 200 domestic cats under controlled feeding conditions, against the major fish-oil brands.

 

91% showed a first-choice preference for Fureeze.

 

And from owners who've lived where you are:

 

⭐⭐⭐⭐⭐ "Pepper's spine was getting bonier every month and her bloods kept saying 'stable'. Since adding one snap-pack to her renal food each day, she's held her weight for two rechecks running — and I've stopped dreading the phone call."

— Helen T., Verified Buyer, Brisbane

 

⭐⭐⭐⭐⭐ "Tom is stage 3. His water bowl used to be empty by lunch. After a few weeks of daily use he seems more settled, and the last recheck was the first one that didn't come with a new medication."

— Danielle P., Verified Buyer, London

 

⭐⭐⭐⭐⭐ "We tried bottled fish oil before, but the smell made Oscar walk away from dinner. He accepts these snap-packs mixed into his wet food, and I love that there is no measuring or guessing."

— Laura C., Verified Buyer, New York

 

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What You're Actually Buying

A spine you can't feel through her coat.

 

A water bowl that's still half full at dinner.

 

A recheck that isn't the worst sixty seconds of your week.

 

Her on your chest after dinner, instead of curled up by the water bowl.

 

You've had those weeks. The difference now is you're supporting all three problems, not one.

 

What it takes: one snap-pack a day on the renal food she already eats. No pump, no fridge, no second product.

 

How long: one recheck cycle. That's the trial window, and it's why the guarantee is 90 days.

 

If I'm wrong: send it back inside 90 days, every dollar refunded.

Start Before the Next Recheck, Not After

You can't control what the number does. You can control what her kidney is getting on the ninety days in between — which is where this disease is actually won or lost.

 

New customers: Up to 50% off your first box + free shipping + free tote bag + free dental supplement

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Kayla Brooks is an Australian based vet nurse and lifelong cat owner. This article includes affiliate links; Fureeze provided product for review but did not approve the final copy. Always consult your vet before introducing a new supplement, especially if your cat is on medication, has pancreatitis, or is pregnant.

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