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KIDNEY VALUES · CATS

Cat creatinine levels and BUN: how to read your cat’s kidney values

Creatinine and BUN are the two classic kidney values on a cat’s chemistry panel. Here is what each one reflects, how the IRIS stages use creatinine, and why a value inside the interval can still matter.

Written by the AI DiagAnimals editorial teamReviewed by the AI DiagAnimals TeamUpdated Our editorial policy

The essentials

Creatinine and BUN (blood urea nitrogen) are waste products cleared by the kidneys. Creatinine depends on muscle mass and rises late, often only after much of the kidney function is lost. BUN also changes with meals, hydration and digestive bleeding. Read together, with SDMA, the urinalysis and the trend over time, they describe kidney function far better than either value alone.

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What creatinine and BUN measure

Creatinine comes from the normal breakdown of muscle. It is produced at a fairly steady rate and filtered by the kidneys, so its blood level rises when filtration falls. Because it depends on muscle, thin cats that have lost muscle can have a reassuring creatinine despite reduced kidney function [1].

BUN (urea nitrogen, called urea in Europe) is made by the liver from protein breakdown and also cleared by the kidneys. It rises with reduced filtration, but also after a protein-rich meal, with dehydration or with bleeding in the upper digestive tract [2].

Creatinine is a fairly insensitive marker: it typically rises only once filtration has dropped substantially [1]. That is why SDMA, which rises earlier, is often measured alongside it.

How to read the creatinine line

A value inside the interval is not always the end of the story, as this example shows.

An annotated line from a lab report · Illustrative example
AbbreviationResultUnitLaboratory intervalFlag
CREA Creatinine1.9mg/dL0.9–2.2–
  1. Abbreviation CREA or CREAT: creatinine.
  2. Result 1.9 mg/dL, within this laboratory’s interval.
  3. Unit mg/dL in the United States, µmol/L in Europe: 1.9 mg/dL ≈ 168 µmol/L. Use the converter below.
  4. Laboratory interval The example uses the cat interval of the Merck Veterinary Manual [3].
  5. Flag No flag. Yet IRIS places stable cats with a creatinine of 1.6–2.8 mg/dL in stage 2 when chronic kidney disease is confirmed [4].

Unit converter

Equivalent values

  • Creatinine, µmol/L–
  • Creatinine, mg/L–

Conversion only changes the unit. Compare the result with the interval printed by the laboratory that measured it.

Normal cat creatinine levels and the IRIS stages

There is no single normal creatinine for cats: each laboratory sets its own interval, for example 0.9–2.2 mg/dL (80–194 µmol/L) in the Merck Veterinary Manual [3]. For cats already diagnosed with stable chronic kidney disease, the International Renal Interest Society (IRIS) uses fixed thresholds on fasting creatinine and SDMA [4].

IRIS Staging of CKD, modified 2026 [4]. Staging applies only to stable, well-hydrated cats with confirmed chronic kidney disease.
IRIS stage (cats)Creatinine mg/dLCreatinine µmol/LSDMA µg/dL
Stage 1< 1.6< 140< 18
Stage 21.6–2.8140–25018–25
Stage 32.9–5.0251–44026–38
Stage 4> 5.0> 440> 38

IRIS then adds two substages: urine protein (UPC below 0.2 non-proteinuric, 0.2–0.4 borderline, above 0.4 proteinuric in cats) and blood pressure [4]. Healthy Birman cats can have higher creatinine and SDMA, with up to 20% outside laboratory intervals [4].

Why the trend matters more than one value

Creatinine varies less within one cat over time than between cats, so following your own cat’s values is more sensitive than comparing them with a population interval [1]. A rise of more than about 0.3 mg/dL supports declining filtration, although this can sit within the analytical variation of some analysers [1].

To confirm stability before staging, IRIS suggests repeating creatinine and/or SDMA after 2 to 4 weeks; changes below 20 to 25% indicate a stable situation [5]. Repeating on the same laboratory makes the comparison more reliable.

BUN and creatinine together: the ratio and what it suggests

BUNCreatinineWhat it can point to [2]
↑NormalProtein-rich meal, upper digestive bleeding, early dehydration.
↑↑Reduced filtration, from before the kidney (dehydration), the kidney itself or after it (urinary blockage).
Normal or ↓↑Very muscular cat, low-protein diet, reduced liver production of urea.

Some reports print a BUN/creatinine ratio. It is a shortcut for this same comparison, and it is interpreted with the clinical picture rather than on its own.

What can change creatinine and BUN

  • Dehydration, which lowers filtration and raises both values [2, 5].
  • Muscle loss, which lowers creatinine and can hide reduced function [1].
  • A recent meal, which can raise BUN and slightly raise creatinine; IRIS stages on fasting values [2, 5].

The values often read with creatinine

SDMA

Rises earlier than creatinine and does not depend on muscle mass.

Read the article

Urinalysis

Urine concentration (USG) and protein (UPC) show how the kidneys are coping [4].

Read the article

Cat blood work overview

All the lines of a cat’s CBC and chemistry panel.

Read the article

For dogs, see creatinine in dogs and potassium in dogs and cats. En français : la créatinine chez le chat et l’urée chez le chat et le chien.

Questions to ask your veterinarian

  1. Is my cat’s creatinine rising compared with previous results, even within the interval?
  2. What do the SDMA, BUN and urinalysis add?
  3. Was my cat fasted and well hydrated when the sample was taken?
  4. If kidney disease is confirmed, which IRIS stage and substages apply?
  5. When should we repeat the tests, and on which laboratory?
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Frequently asked questions

What is considered a high creatinine level in cats?

A value above your laboratory’s interval is flagged high, for example above 2.2 mg/dL in the Merck Veterinary Manual table [3]. For cats with confirmed chronic kidney disease, IRIS uses 1.6 mg/dL (140 µmol/L) as the start of stage 2 [4].

Can creatinine levels go down in cats?

Yes. If the cause is temporary, such as dehydration or an acute kidney injury that recovers, creatinine can fall back. In chronic kidney disease, the aim of follow-up is to keep the values as stable as possible.

What is a worrisome creatinine level?

There is no single cut-off: a rising trend, a value in a higher IRIS stage, or any value in a cat that is unwell all deserve prompt discussion with your vet [1, 4].

What is a normal BUN/creatinine ratio in cats?

The ratio is a way to compare the two values. It has no universal normal range and is read with the cat’s hydration, diet and history [2].

How can I lower my cat’s BUN?

BUN reflects its causes: hydration, diet and kidney function. Your vet may adjust fluids or diet depending on the situation. Do not change the diet or give supplements without advice.

Sources

  1. eClinPath, Cornell University College of Veterinary Medicine. Creatinine. eclinpath.com/chemistry/kidney/creatinine
  2. eClinPath, Cornell University College of Veterinary Medicine. Urea nitrogen. eclinpath.com/chemistry/kidney/urea-nitrogen
  3. Merck Veterinary Manual. Serum biochemical analysis reference ranges. merckvetmanual.com/reference-values-and-conversion-tables/reference-guides/serum-biochemical-analysis-reference-ranges
  4. International Renal Interest Society (IRIS). IRIS Staging of CKD (modified 2026). iris-kidney.com/s/IRIS_staging_guidelines-2026.pdf
  5. International Renal Interest Society (IRIS). IRIS Staging System. iris-kidney.com/iris-staging-system

Laboratory methods and reference intervals vary. This article explains; it does not diagnose. For a decision about your pet, use the original report and talk to your veterinarian. Our editorial policy.

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