Cat Kidney Disease: What Early Screening Actually Looks For

By Morgan Reyes

Not eating, repeated vomiting, straining to urinate with little or nothing coming out, or sudden changes in vision or balance: those are same-day vet or emergency-clinic problems, not screening questions. The emergency section has the detail.

A Normal Creatinine Doesn't Close the Question

Early kidney disease in cats is usually silent, and a real screen looks at five things together and repeats them: creatinine, SDMA, how concentrated the urine is, urine protein, and blood pressure. One normal number is not an all-clear, and two that disagree are not a verdict.

Most pages on this topic list the signs (thirst, weight loss, vomiting) and stop, but those describe a cat well along already. This one starts later, with a lab sheet in your hand or a vet's passing remark ("her SDMA is a bit up", "creatinine is at the top of normal", "her urine is a bit dilute"), and covers what the numbers mean and what a complete work-up includes.

The standard vets stage kidney disease against is published by IRIS, the International Renal Interest Society, an independent non-profit. The most recent cat-specific consensus is the 2026 iCatCare guideline. The staging numbers below are IRIS's own, and the screening advice is iCatCare's, quoted as written.

Why "drinking more" isn't screening

A cat drinking more is a real signal, but it is a late-ish and non-specific one. Cornell's Feline Health Center explains why: in early kidney disease "it is very common for cats to show no obvious clinical signs, as their body is able to compensate for the decrease in kidney function." Extra drinking and urine come as the kidneys lose the ability to concentrate urine. The MSD Veterinary Manual puts the timing plainly: these are usually the earliest signs, but they "do not begin to appear until Stage II or III," and they "may signal other diseases as well."

International Cat Care lists the most common causes of increased thirst as kidney disease, diabetes mellitus, hyperthyroidism and high blood calcium, with others such as liver disease behind them. Extra thirst says "something is off" and stops there.

Here is International Cat Care's method for turning "drinking more" into a number:

1. Fill the water bowl (or every bowl) to the brim.
2. Measure what is left 24 hours later and subtract it from the starting amount.
3. Compare with your cat's weight: more than 100 ml per kg of body weight a day is drinking more than usual.

For a 4 kg cat that is 400 ml, a bit under two cups. Shared bowls or outdoor drinking make the number unreliable; International Cat Care suggests separating the cats for the 24 hours if that doesn't upset anyone.

A cat on wet food may rarely, if ever, be seen drinking, so "I never see her at the bowl" proves nothing either. International Cat Care's ask is simple: any cat drinking more than usual should be seen by a vet, and a fresh urine sample brought along helps. Whether a fountain changes how much your cat drinks is a separate question: see what actually moves urine concentration.

What a complete early screen includes

The 2026 iCatCare guideline recommends screening from age 7: an annual examination for cats aged 7 to 10, and preferably twice a year for cats over 10. Screening means "regular body weight measurement, blood examination and urinalysis, even in asymptomatic cats."

Does it find anything? Two prospective studies at Ghent University, cited in the guideline, found kidney disease at IRIS stage 2 or higher in 8% of apparently healthy older cats (15% of the seniors versus 3% of the mature adults). And among cats who screened healthy the first time, a further 24% of those aged 11 and over, and 8% of those aged 7 to 10, developed azotaemia (raised waste products in the blood) within 2 years. The guideline's conclusion: even a clean first result should be followed by serial results, because the trend is information.

For SDMA basics and the full list of tests a senior wellness visit should include, see the senior wellness visit checklist. Here the focus is narrower: what the kidney-specific pieces can and cannot see.

Add body weight and a muscle condition score and you have the whole picture. As Cornell puts it: "there is no single test that can give a veterinarian a complete picture of kidney function."

Older guidance was blunter about SDMA. The 2016 ISFM consensus said it "cannot currently be recommended as a single screening test for CKD," though useful for supporting a diagnosis. The 2026 iCatCare update is softer: initial studies suggested SDMA rose well ahead of creatinine, but later research found the correlation of each marker with actual filtration rate to be comparable.

Why creatinine misses a thin cat

Creatinine can look normal in a cat whose kidneys are already filtering poorly, because how much of it a body produces depends on muscle mass. Paepe and Daminet's review says exactly that: the daily production rate of creatinine "depends on muscle mass, which may be of clinical importance in geriatric cats with age-related muscle wasting or when muscle mass gradually declines during CKD progression."

Cornell states the consequence in one line: "a very thin cat may have normal blood creatinine levels despite decreased kidney function." The iCatCare guideline agrees that creatinine is influenced by muscle mass and hydration, and adds that in older cats it runs lower, "possibly due to loss of lean muscle mass," so the upper limit of the lab's reference interval "needs to be adjusted downwards." A value that sits comfortably inside a generic range can be high for a 14-year-old.

The same guideline says weight loss is common in cats with kidney disease and may be the only sign, and that "insidious weight loss and loss of muscle mass may go unnoticed by caregivers or be incorrectly attributed to age." One large study it cites found a median loss of 8.9% of body weight in the 12 months before diagnosis, with weight loss already present 3 years before.

At home:

• Weigh your cat regularly on the same scale, and keep the numbers. A trend across visits beats any single reading.
• Ask about muscle condition. The iCatCare guideline treats body and muscle condition scores as part of assessing a cat, so ask what your cat's muscle score is and whether it has changed.
• Ask what the reference range was. "Normal" means inside the lab's range, and creatinine "close to the upper reference limit" is worth a second look in a thin senior.

IRIS stages, in a table

IRIS says staging "is undertaken following diagnosis," and is "based initially on fasting blood creatinine or fasting blood SDMA concentration or (preferably) both assessed on at least two occasions in a hydrated, stable patient." The cat is then substaged by urine protein and blood pressure. These are the cat columns of the IRIS staging table (modified 2026):

Two IRIS comments matter most for an early result:

Stage 1 can have a normal creatinine. IRIS describes it as "normal blood creatinine or normal or mild increase blood SDMA," with "some other renal abnormality present," and gives examples: inadequate urinary concentrating ability with no non-kidney explanation (in cats, not dogs), abnormal findings on palpation or imaging, protein in the urine that comes from the kidney, or "increasing blood creatinine or SDMA concentrations in samples collected serially." It adds that "persistently elevated blood SDMA concentration (above 14 ug/dl) may be used to diagnose early CKD."

Stage 2 is where creatinine's weakness is written into the standard. IRIS says the lower end of the stage 2 range sits inside the reference range for many laboratories, "but the insensitivity of creatinine concentration as a screening test means that patients with creatinine values close to the upper reference limit often have excretory failure." Clinical signs are "usually mild or absent."

Once a cat is staged, IRIS adds two substage labels:

IRIS says its SDMA recommendations "are based on published literature which utilizes proprietary IDEXX technology for measuring SDMA," and that "it is not known if other assays will provide equivalent results." If your cat's SDMA was run at a different lab, ask your vet whether the IRIS numbers apply to that lab's method.

When SDMA and creatinine disagree

IRIS's rule for discordant results is to retest both in 2 to 4 weeks, and if they still disagree, to go with the higher stage. The IRIS pocket guide says: "In the case of staging discrepancy between creatinine and SDMA, consider patient muscle mass and retesting both in 2-4 weeks. If values are persistently discordant, consider assigning the patient to the higher stage." The iCatCare guideline repeats it in nearly the same words.

For a cat with a creatinine that looks like stage 1 (below 140 umol/l), IRIS's staging document goes further:

• SDMA persistently above 18 ug/dl: stage as IRIS stage 2.
• Creatinine 141 to 250 umol/l and SDMA persistently above 25 ug/dl: stage as IRIS stage 3.
• Creatinine 251 to 440 umol/l and SDMA persistently above 38 ug/dl: stage as IRIS stage 4.

The operative word is "persistently": one high SDMA is a reason to look again, not a diagnosis.

Both guidelines name non-kidney reasons the two markers can disagree, and they run in different directions:

• Hyperthyroidism. The iCatCare guideline says it "may increase the GFR and decrease muscle mass, with the result that creatinine is lowered into the RI" (the reference interval), which can hide kidney disease until the thyroid is treated. A high SDMA before treatment makes kidney disease more likely, but a normal SDMA "does not exclude the development of azotaemia" afterward.
• Lymphoma. IRIS and iCatCare both say it can raise SDMA without a drop in filtration. IRIS's takeaway: "This illustrates the value of having two biomarkers ... which can be interpreted together."
• Diabetes. The iCatCare guideline says cats with diabetes mellitus often have significantly lower SDMA than healthy cats, the reverse problem.
• Dehydration. It pushes creatinine up even when the kidneys are working normally, per Cornell, which is why IRIS wants staging done in a "hydrated, stable" cat.
• Breed. IRIS notes that healthy Birman cats run higher on both creatinine and SDMA, "taking some healthy individuals (up to 20% of Birman cats) outside laboratory reference intervals."

When your two numbers point different ways, ask whether muscle condition is a factor in the creatinine reading, when both get retested (and whether at the same lab), and whether a thyroid check is part of this. A vet who says "let's recheck in a few weeks" after a discordant result is following the standard, not brushing you off. One who has not mentioned urine or blood pressure at all has left part of the screen undone, and it is fair to ask what her urine concentration and urine protein were, and whether her blood pressure has been measured, and how.

Urine and blood pressure: the parts people skip

The blood test gets the attention, but the urine and the pressure reading often tell the story earlier.

Urine concentration

The iCatCare guideline calls loss of urine-concentrating ability "one of the earliest manifestations of a decline in kidney function" and says that "a USG below 1.035 should raise suspicion for decreased urine-concentrating ability and early-stage CKD, even when other markers of kidney function remain within the RI." Paepe and Daminet give the mechanism: over two-thirds of functional kidney mass must be lost before the kidneys lose their concentrating ability, and over three-quarters before azotaemia develops. So urine can flag a problem before creatinine does.

The guideline states the exceptions itself. Cats with early kidney disease and mildly raised creatinine can still concentrate normally (USG 1.035 or above). And "unless a cat is being fed a high-moisture diet, or has another reason for producing dilute urine," a low reading should prompt a repeat and further investigation "if persistent." IRIS's pocket guide adds a footnote to the same effect: some cats can produce concentrated urine despite kidney-related azotaemia. So a dilute sample is a reason to repeat and look further, not a diagnosis, and a concentrated one is not an all-clear.

Urine protein

IRIS wants the urine protein:creatinine ratio (UPC) measured in cats with kidney disease, and warns that "standard urine dipsticks can be insensitive." Paepe and Daminet are more specific: dipsticks "only reliably detect severe feline proteinuria," and in cats with low-level protein loss, false positives and false negatives are common. A "negative dipstick" therefore doesn't clear protein loss. IRIS also asks for at least two samples collected 2 weeks or more apart for substaging.

Blood pressure

The kidneys help regulate blood pressure, and Cornell notes that in cats with kidney disease this can be disrupted; high pressure "can lead to sudden changes in vision, neurologic abnormalities such as disorientation and weakness, or heart issues." The iCatCare guideline reports that eye damage from high blood pressure is present in up to 80% of cats with systemic hypertension.

A frightened cat can read high, and IRIS's answer is repetition: "Patients should be acclimatized to the measurement conditions and multiple measurements taken," ideally on separate days, or the same visit with at least 2 hours between determinations. The iCatCare guideline recommends taking blood pressure as the first part of the exam, "in as calm a manner as possible, with minimal handling." A calm cat gives a truer number, which is a practical reason to sort out the trip itself: getting a cat to the vet with less stress is worth doing before a screening visit, not after.

The emergency line: what is not "early screening"

Chronic kidney disease builds over months to years. A sudden change is a different category and should be treated as one. These are same-day calls to your vet or an emergency clinic:

• Not eating, or repeated vomiting, in a cat with known or suspected kidney disease. The iCatCare guideline lists nausea, vomiting and inappetence among the signs of kidney disease, more common at higher stages, and the MSD manual notes that cats that are dehydrated or not eating may need intravenous fluids or a feeding tube. None of the guidelines quoted here sets an hour count for "not eating," so don't wait for one.
• Straining in the litter box, or trying to urinate with little or nothing coming out. That is a different problem from chronic kidney disease. MSD says a urinary tract obstruction in a male cat "should be considered a medical emergency and requires immediate veterinary attention." The full picture is in our guide to cat behaviour and the one litter-box emergency. Early kidney disease tends to mean more urine, not less, and a cat producing little or none needs an urgent exam whatever the cause.
• Sudden blindness, bumping into things, disorientation or weakness, especially in a cat known to have high blood pressure. When eye damage from high pressure is already present, the iCatCare guideline says prompt treatment is indicated.
• Any part of a lily. MSD: ingestion of a small amount of any part of a lily (flower, leaf, pollen or water) "can cause a severe kidney injury in cats." Call now, before signs appear.

Acute injury has its own signs, which MSD lists as loss of appetite, depression, dehydration, mouth sores, vomiting, diarrhea and a smaller-than-normal volume of urine. If you can't tell which problem you are looking at, the answer is the same: call.

Bottom line

Bottom line: early kidney disease in cats usually shows nothing, so screening has to look for it: creatinine and SDMA together, urine concentration, urine protein and blood pressure, repeated over time. A normal creatinine does not rule out disease, particularly in a thin older cat, and two markers that disagree get retested in 2 to 4 weeks.

What to bring to the visit, and what to ask for:

• Your cat's weight history, any change in drinking, and a 24-hour water measurement if you can take one, plus a fresh urine sample if your clinic wants one.
• A request for creatinine and SDMA together, a urine specific gravity, a urine protein:creatinine ratio, and a blood pressure reading.
• A plan for when to repeat if the markers disagree, and which lab runs the repeat.

FAQ

Can a cat have kidney disease with a normal creatinine?

Yes. IRIS stage 1 is defined by a creatinine below 140 umol/l plus some other kidney abnormality, and IRIS notes that in stage 2 the insensitivity of creatinine as a screening test means cats with values close to the upper reference limit often already have excretory failure. Creatinine also depends on muscle mass, so a thin cat can look normal on it.

My cat's SDMA is high but the creatinine is normal. What happens next?

IRIS says to consider muscle mass and retest both markers in 2 to 4 weeks. If the SDMA stays above 18 ug/dl in a cat whose creatinine is below 140 umol/l, IRIS says to stage the cat as stage 2. Non-kidney causes such as hyperthyroidism and lymphoma can raise SDMA, so the retest and the rest of the work-up matter.

How much water is too much for a cat?

International Cat Care says a cat drinking more than 100 ml per kg of body weight a day is drinking more than usual, measured by filling the bowl and subtracting what is left after 24 hours. It also says any cat drinking more than usual should be seen by a vet. Kidney disease is only one cause; diabetes, an overactive thyroid and high blood calcium are others.

At what age should cats be screened for kidney disease?

The 2026 iCatCare consensus guidelines recommend screening from age 7: annual check-ups from 7 to 10, and preferably twice a year for cats over 10. Screening means regular body weight measurement, blood examination and urinalysis, even in a cat with no signs.

Keep reading

• What to Ask For at a Senior Pet's Wellness Visit. The full test table, including SDMA basics.
• Cat Water Fountains and Urinary Health. What changes how concentrated a cat's urine is.
• Getting a Cat to the Vet Without the Carrier Panic. Blood pressure and urine samples get easier with a calmer cat.
• Why Cats Get Less Care Than Dogs. The pattern behind missed screening visits.
• What Pet Owners Actually Do About the Cost of Vet Care. For when the next step worries you on price.

A Note on Scope

This guide explains published veterinary guidelines on how kidney disease in cats is screened for and staged. It is not veterinary advice, does not diagnose any individual cat, and does not cover treatment, diet or medication. Reference ranges vary by laboratory, and your cat's results are for your vet to interpret. If your cat shows any of the emergency signs above, contact a vet or emergency clinic now.

Sources

• IRIS, "IRIS Staging of CKD (Modified 2026)". Fetched 29 September 2026. Cat staging table, discrepancy rules, stage 1 and 2 comments, Birman note, assay caveat, UPC and blood pressure substages.
• IRIS, "Diagnosing, Staging, and Treating Chronic Kidney Disease in Dogs and Cats" pocket guide (June 2026). Fetched 29 September 2026. 2 to 4 week retest wording, USG cutoff for cats.
• Taylor S, Finch N, Caney S et al., "2026 iCatCare consensus guidelines on the diagnosis and management of chronic kidney disease in cats," Journal of Feline Medicine and Surgery 28(9), 2026. Fetched 29 September 2026. Screening age and frequency, Ghent screening figures, creatinine and SDMA limitations, USG below 1.035, blood pressure handling.
• Sparkes AH et al., "ISFM Consensus Guidelines on the Diagnosis and Management of Feline Chronic Kidney Disease," Journal of Feline Medicine and Surgery 18(3):219-239, 2016. Fetched 29 September 2026. SDMA-as-single-screening-test wording; superseded on SDMA by the 2026 guideline above.
• Paepe D, Daminet S, "Feline CKD: Diagnosis, staging and screening - what is recommended?" Journal of Feline Medicine and Surgery 15(1 Suppl):15-27, 2013. Fetched 29 September 2026. Creatinine production and muscle mass, two-thirds and three-quarters loss figures, dipstick limits. Predates SDMA in IRIS staging, so used for mechanism only.
• Cornell Feline Health Center, "Chronic Kidney Disease" (updated January 2025). Fetched 29 September 2026. Early compensation, thin-cat creatinine point, hypertension signs, "no single test."
• MSD Veterinary Manual (Cat Owners), "Noninfectious Diseases of the Urinary System of Cats". Fetched 29 September 2026. When thirst appears, acute kidney injury signs, lily warning, male-cat obstruction emergency.
• International Cat Care, "Increased thirst and drinking" (updated 26 September 2025). Fetched 29 September 2026. Causes of increased thirst, 24-hour measuring method, 100 ml per kg threshold.