The water bowl needs filling more often than it used to. The litter box is heavier, and the clumps are bigger. Your cat is thirteen, her coat looks a little rough, and when you picked her up last week she felt lighter than she looks.
That is the picture nearly every owner arrives with. Kidney disease is common in older cats: VCA Animal Hospitals puts it at "30% to 40% of cats over 10 years of age and 81% of cats over 15 years."¹ But the symptom list you will find in four seconds has a problem nobody mentions. By the time a cat produces any of those signs, VCA states, "at least two-thirds (67% to 70%) of the kidneys must be dysfunctional."¹
So the honest version of "what are the early signs of kidney disease in cats" is uncomfortable: the signs you can see are not early. Below are the signs as the sources state them, the diseases that produce the same picture in a senior cat, the one thing you can actually measure tonight, and what the number to bring your vet really is.
Key takeaways
- The signs you can see are not early signs. VCA states that "at least two-thirds (67% to 70%) of the kidneys must be dysfunctional before any clinical signs are seen," and Merck adds that cats usually show nothing until their kidneys work at "less than 25% of their usual capacity."¹³
- The genuinely earliest sign is a lab value, not a behaviour. Per VCA, dilute urine — a low urine specific gravity — "is the earliest sign of kidney disease," which is why a urinalysis in a well-looking senior cat finds things watching cannot.¹
- Thirst is measurable, and almost nobody measures it. International Cat Care puts the flag at more than 100 mL per kg of body weight per day, which is roughly 400 mL for a 4 kg cat.⁴
- Weight loss starts years before the diagnosis. In a study of 569 cats with CKD, loss was detectable as early as three years out, and among those weighed at both time points the median fall was 8.9% in the final 12 months.⁶
What are the signs of kidney disease in cats?
VCA Animal Hospitals splits them into two sets. The early ones are "weight loss, poor coat quality, variable appetite, increased water consumption and urination." The advanced ones are "poor appetite, lethargy, depression, vomiting, diarrhea, anemia, bad breath associated with mouth ulcers."¹
The Merck Veterinary Manual is narrower about which of these an owner notices first: "Usually, the earliest signs are excessive thirst and urination." As the disease advances, Merck lists "loss of appetite, weight loss, dehydration, sores in the mouth, sluggishness, vomiting, and diarrhea."³
Cornell's Feline Health Center describes the same progression mechanically. Failing kidneys cannot concentrate urine, so cats "urinate greater volumes and drink more water to compensate"; protein and vitamins are lost in that urine, which contributes to "abnormal metabolism and loss of appetite." Later, affected cats "appear lethargic, unkempt, and lose weight."²
Two of those signs are really one sign seen from either end. The cat is not thirsty because something made her thirsty — she is drinking to replace water she cannot stop losing. That matters for what you measure: the litter box and the water bowl are two readings of the same failure, and either one will do.
| Stage | What the Merck Veterinary Manual says you would see | What that means at home |
|---|---|---|
| Stage I | No signs; kidney damage present but compensated | Nothing to notice. Only a blood or urine test finds this. |
| Stage II | "Cat usually shows no signs but may be urinating more than previously" | Slightly heavier litter box. Easy to miss, and easy to explain away. |
| Stage III | "Excessive thirst and urination" | The bowl empties faster and the box is obviously heavier. This is usually when owners search. |
| Stage IV | "Vomiting, depression, loss of appetite, weight loss, dehydration, mouth sores, diarrhea" | A visibly unwell cat. Needs veterinary care now, not an appointment next week. |
Stage descriptions quoted from the Merck Veterinary Manual's owner reference.³ These broadly follow the IRIS staging scheme, which becomes the thing to know once a cat is diagnosed rather than before.
Why are the "early" signs already late?
Because the kidneys are built with enormous spare capacity, and they spend it silently. VCA puts the threshold plainly: "The kidneys have a large amount of spare capacity to perform their various functions, so at least two-thirds (67% to 70%) of the kidneys must be dysfunctional before any clinical signs are seen."¹ Merck arrives at much the same place from the other direction — cats "usually have no signs of kidney disease until they are at Stages III or IV, when their kidneys are working at less than 25% of their usual capacity."³
There is a nastier structural feature. VCA notes that "after approximately two-thirds of the kidney tissues fail, the amount of waste in the bloodstream increases quickly and severe disease seems to begin suddenly."¹ The disease does not feel gradual to the owner even though it is. It looks like nothing for years, then looks like a crisis in a fortnight.
Now the part that reorders everything. Cornell states: "Creatinine concentrations in the blood do not generally rise until a cat has lost almost 75% of their renal function, while SDMA elevations are detectable when about 40% of kidney function is lost."² Creatinine is the number most owners have heard of. It is also the last of the three to move — though the 67–70% and 75% figures come from different sources, so read their order as close rather than settled. The gap to SDMA is the unambiguous one.
One signal is earlier than all of them, and it is not a behaviour. VCA: "A low USpG means the urine is diluted (watery), which is the earliest sign of kidney disease."¹ Urine specific gravity is measured on a urine sample, in a clinic, from a cat who looks well. That is the whole argument for testing senior cats before anything is wrong — and it is why no amount of careful watching substitutes for it.
How much water is too much for a cat?
International Cat Care gives a number: "A cat drinking more than 100ml per kg of their body weight daily is drinking more water than usual."⁴ For a 4 kg cat — about 8.8 lb, a fairly typical adult — that is 400 mL a day, a bit under two US cups. Cross that and it is worth a vet visit whatever else seems fine.
For context on the other end, a 2025 scoping review in the Journal of Animal Science reports that "across an assessment of five groups of healthy domestic cats, 23 to 51 mL/kg BW of total water was consumed daily."⁵ Read that figure carefully: it is total water intake, which counts the moisture in food as well as what the cat drinks. The same review states that "cats fed a wet diet have higher TWI but lower FWI compared to cats fed a dry diet" — more water overall, less of it from the bowl.⁵ So the healthy band and the 100 mL/kg flag are not two ends of one scale, and a low bowl reading in a wet-fed cat proves nothing.
International Cat Care gives the method: "filling their water bowl(s) to the brim, measuring the amount of water left at the end of the 24 hours, and taking this away from the volume in the full water bowl(s)."⁴ Do it three days running; one day means nothing.
Two practical traps. If more than one cat drinks from that bowl, the number is a household number, not a cat number — write that down rather than treating it as hers. And if she also drinks from taps, the shower tray or a pond, say so; the bowl reading understates her by an unknown amount, which is still worth telling your vet.
Is weight loss a sign of kidney disease in cats?
Yes — and it is the sign that starts earliest by a wide margin. A 2016 study in the Journal of Veterinary Internal Medicine reviewed the records of 569 cats with CKD from six US veterinary practices and found that "weight loss was identified as early as 3 years before diagnosis of CKD."⁶ Three years — in an animal whose median age at diagnosis was 14.9 years.
The final year is steeper. Among the 273 cats with weight recorded at both time points, "the median percentage change in body weight ... was −8.9%" over the 12 months before diagnosis.⁶ On a 4.5 kg cat that is 400 g. It is plain on a kitchen scale and close to invisible in a photograph, which is exactly why it goes unnoticed.
Weight also carries prognosis. Median body weight at diagnosis was 4.2 kg, and cats above that median "had a significantly longer survival time compared to cats with a body weight lower than the group median (P < .0001)."⁶ Thinner at diagnosis meant shorter survival.
The authors' own conclusion is the practical one: "Tracking body weight may help clinicians in earlier diagnosis of CKD in cats and earlier institution of dietary management and other medical treatments."⁶ There is a second reason to keep that record. Cornell notes that "a very thin cat may have normal blood creatinine levels despite decreased kidney function"² — so a cat who has lost muscle can post a reassuring number she has not earned. Your weight history is context the blood test cannot supply.
What else causes the same signs?
Three other things, mainly, and they are common in exactly the same cats. International Cat Care names them: "The most common causes of increased thirst and drinking are: Kidney disease, Diabetes mellitus, Hyperthyroidism, High blood calcium levels."⁴ A senior cat drinking more, losing weight and eating oddly fits all four, and you cannot tell them apart from the sofa.
The overlap is not just inconvenient — one disease actively conceals another. The FDA explains that in hyperthyroid cats, "the high level of thyroid hormones increases the blood flow to the kidneys, which helps their kidneys and may even hide kidney disease." Treat the thyroid and "the blood flow to the kidneys returns to normal and the kidney function in some cats will worsen."⁷ The FDA adds the blunt summary: "Older cats often have both hyperthyroidism and kidney disease, and treating these cats is a delicate balancing act."⁷
| Condition | Shares with kidney disease | What tends to differ | How it is actually told apart |
|---|---|---|---|
| Chronic kidney disease | Thirst, urination, weight loss, poor coat, variable appetite¹ | Dilute urine; mouth ulcers and anaemia later¹ | Urine specific gravity, creatinine, SDMA, urine protein² |
| Diabetes mellitus | Thirst, urination, weight loss⁹ | Glucose spills into the urine above roughly 280 mg/dL in cats; appetite often increased, though Merck records "up to 50% of cats with diabetes mellitus have a decreased appetite"⁹ | Blood and urine glucose testing. See cat diabetes symptoms. |
| Hyperthyroidism | Thirst, urination, weight loss, unkempt coat, vomiting⁷ | "Weight loss despite an increased appetite"; hyperactivity⁷ | Thyroxine (T4). Note it can mask kidney disease.⁷ See managing cat hyperthyroidism. |
| High blood calcium | Thirst and urination⁴ | Often nothing else outwardly — which is why it turns up on bloodwork, not at home | Serum calcium on a routine blood panel |
A symptom list cannot separate these four, and a good one does not pretend to. What it can do is tell you which numbers to arrive with, so the visit starts from evidence instead of recollection.
When should you call the vet about these signs?
Book an appointment for increased drinking or urination, gradual weight loss, or a coat that has gone rough. None is an emergency; all mean the disease is established rather than starting.
Go now — same day, out of hours if necessary — if your cat is vomiting repeatedly, will not eat or drink, has mouth ulcers or foul breath, or has become weak or unsteady. Merck lists that cluster under Stage IV, the most advanced stage.³ Sudden vision change or disorientation also warrants an urgent call. Cornell names "sudden changes in vision, neurologic abnormalities such as disorientation and weakness, or heart issues" among the complications of feline CKD,² and Merck reports that "about 20% of cats with longterm kidney disease have elevated blood pressure."³
And one case is a true emergency with a clock on it, unrelated to the slow disease above. If your cat may have chewed, licked or groomed a lily, or drunk its vase water, call immediately. The ASPCA states that in lilies of the Lilium and Hemerocallis genera, "all parts of the plant are toxic and small amounts can cause severe injury to the kidneys," and that poisoning is "often fatal if treatment is delayed longer than 18 hours after ingestion."⁸ That is acute kidney injury, not the chronic disease described here, and it is treatable early and often not treatable late.
How do you track the signs so the pattern is visible?
Three measurements, none taking a minute a day: water, weight, and urine volume. Recorded for two weeks they turn "she's been drinking more lately" into a number your vet can use, and for a year they do the thing the Freeman study says matters — make a slow decline visible while it is still slow.⁶
- Water, daily. Fill to a marked line at a fixed time and measure what is left 24 hours later. Note how many cats share the bowl, and any tap or shower drinking.
- Weight, weekly. Same scale, same day, in grams. A 400 g loss on a 4.5 kg cat is the median year before diagnosis; that is what you are looking for.⁶
- Urine, daily. Count clumps, or weigh what you scoop. Crude, but consistent — and consistency makes a trend readable.
- Appetite and energy, daily. A 1-to-5 rating beats "good" or "picky", because a series of numbers shows a slide that adjectives hide.
This is not carelessness. Owners are excellent observers and terrible historians: "she's been drinking more" is a real observation with no timeline attached, and where two people share the feeding and the scooping, neither one holds the whole picture. Cats make it worse by design: they conceal illness until concealment stops working, the same reason pain in cats goes unnoticed for so long.
Start the record before the diagnosis, not after. If the tests come back clear, you have a baseline for next time. If they do not, the record keeps earning immediately — our guide to what to log for a cat with chronic kidney disease picks up exactly where this leaves off, with the daily tracking, the fluids and the staging.
Veterinary medical disclaimer: SteadyTails is a logging and coordination tool, not a substitute for veterinary care. Nothing on this page is a diagnosis or a treatment plan. Kidney disease in cats cannot be confirmed or ruled out at home: it requires blood and urine testing, and the signs described here overlap substantially with diabetes mellitus, hyperthyroidism and high blood calcium, which only your veterinarian can tell apart. Do not change your cat's diet, withhold water, or give any medication or supplement for suspected kidney disease without veterinary advice. If your cat is vomiting repeatedly, refusing food, not drinking, has mouth sores, has become weak or unsteady, or has sudden vision changes or disorientation, contact your veterinarian or an emergency animal hospital immediately. If your cat may have been exposed to a lily of any kind, treat it as an emergency: the ASPCA Animal Poison Control Center is available on (888) 426-4435, and lily poisoning is often fatal once treatment is delayed beyond 18 hours.⁸
"How long has she been drinking like this?"
It is the first question your vet will ask, and the honest answer is usually a shrug. SteadyTails turns the things you notice into things you can count: water and weight logged in seconds, daily wellbeing ratings for appetite, energy and comfort, trends over 7 and 30 days, and one shared timeline the whole household writes to — so the year before the appointment arrives as evidence instead of a guess. Coming soon to iOS and Android.
Join the SteadyTails waitlist →References
- VCA Animal Hospitals. Chronic Kidney Disease in Cats — "The kidneys have a large amount of spare capacity to perform their various functions, so at least two-thirds (67% to 70%) of the kidneys must be dysfunctional before any clinical signs are seen." "After approximately two-thirds of the kidney tissues fail, the amount of waste in the bloodstream increases quickly and severe disease seems to begin suddenly." Early signs given as "weight loss, poor coat quality, variable appetite, increased water consumption and urination"; advanced signs as "poor appetite, lethargy, depression, vomiting, diarrhea, anemia, bad breath associated with mouth ulcers." "A low USpG means the urine is diluted (watery), which is the earliest sign of kidney disease." "It is mainly a problem in mature and senior cats (seven years and older), affecting 30% to 40% of cats over 10 years of age and 81% of cats over 15 years. Only about 10% of cases occur in cats less than three years old." vcahospitals.com Retrieved 2026-09-27.
- Cornell University College of Veterinary Medicine, Cornell Feline Health Center. Chronic Kidney Disease — CKD "affecting up to 40% of cats over the age of 10 and 80% of cats over the age of 15". "Creatinine concentrations in the blood do not generally rise until a cat has lost almost 75% of their renal function, while SDMA elevations are detectable when about 40% of kidney function is lost." Affected cats "urinate greater volumes and drink more water to compensate"; "The loss of important proteins and vitamins in their urine may contribute to abnormal metabolism and loss of appetite"; they may "appear lethargic, unkempt, and lose weight". Complications include "sudden changes in vision, neurologic abnormalities such as disorientation and weakness, or heart issues". "a very thin cat may have normal blood creatinine levels despite decreased kidney function". Diagnostic tests named: "blood urea nitrogen (BUN), creatinine, and symmetric dimethyl arginine (SDMA)", "urine specific gravity, or USG" and "Urine protein/creatinine ratio, or UPC ratio". "Cats who are diagnosed with IRIS Stage 2 CKD have a mean survival time of two to three years in many studies, while those who are diagnosed at IRIS Stage 4 on average survive less than 6 months." vet.cornell.edu Retrieved 2026-09-27.
- Merck Veterinary Manual. Noninfectious Diseases of the Urinary System of Cats (Cat Owners) — "Chronic kidney disease often continues for many months or years before a cat has any signs." "Cats usually have no signs of kidney disease until they are at Stages III or IV, when their kidneys are working at less than 25% of their usual capacity." "Usually, the earliest signs are excessive thirst and urination." "As the disease progresses over months to years, other problems begin. These include loss of appetite, weight loss, dehydration, sores in the mouth, sluggishness, vomiting, and diarrhea." Stage II: "Cat usually shows no signs but may be urinating more than previously." Stage III: "Excessive thirst and urination". Stage IV: "Vomiting, depression, loss of appetite, weight loss, dehydration, mouth sores, diarrhea." "About 20% of cats with longterm kidney disease have elevated blood pressure (hypertension)." merckvetmanual.com Retrieved 2026-09-27.
- International Cat Care. Increased thirst and drinking — "A cat drinking more than 100ml per kg of their body weight daily is drinking more water than usual." Measurement method: "filling their water bowl(s) to the brim, measuring the amount of water left at the end of the 24 hours, and taking this away from the volume in the full water bowl(s)." "The most common causes of increased thirst and drinking are: Kidney disease, Diabetes mellitus, Hyperthyroidism, High blood calcium levels." icatcare.org Retrieved 2026-09-27.
- Kosmal PAL, Shoveller AK, Gillies G, Armstrong LE. Diet format, protein, amino acids, salt, and osmolytes, as well as water viscosity, affect water consumption in domestic cats: a scoping review of 32 publications (published from 1975 to 2025) on water intake, hydration status, and related health outcomes. Journal of Animal Science, 2025 — "Across an assessment of five groups of healthy domestic cats, 23 to 51 mL/kg BW of total water was consumed daily." Total water intake (TWI) counts dietary moisture as well as free water intake (FWI): "Cats fed a wet diet have higher TWI but lower FWI compared to cats fed a dry diet." pmc.ncbi.nlm.nih.gov Retrieved 2026-09-27.
- Freeman LM, Lachaud MP, Matthews S, Rhodes L, Zollers B. Evaluation of Weight Loss Over Time in Cats with Chronic Kidney Disease. Journal of Veterinary Internal Medicine. 2016 Sep;30(5):1661–1666 — "Five hundred and sixty-nine cats were enrolled in the study" from "6 US veterinary practices". "Median age at diagnosis was 14.9 years (range, 5.0–22.8 years)". "Median body weight for all 569 cats at the time of diagnosis was 4.2 kg (1.6–9.9 kg)". "the median percentage change in body weight for the 273 cats with body weight measurements at both time points was −8.9%" in the 12 months before diagnosis. "weight loss was identified as early as 3 years before diagnosis of CKD". "Cats with a body weight at diagnosis higher than the group median (4.2 kg) had a significantly longer survival time compared to cats with a body weight lower than the group median (P < .0001)". "Tracking body weight may help clinicians in earlier diagnosis of CKD in cats and earlier institution of dietary management and other medical treatments". pmc.ncbi.nlm.nih.gov Retrieved 2026-09-27.
- U.S. Food and Drug Administration. Hyperthyroidism in Cats: There's an FDA-Approved Drug to Treat It (Animal Health Literacy) — hyperthyroidism is "the most common endocrine disease of cats older than 8-years-old". "The most common sign of hyperthyroidism in cats is weight loss despite an increased appetite. Other common signs include vomiting, diarrhea, hyperactivity, drinking and urinating more than normal, and an unkempt hair coat." "the high level of thyroid hormones increases the blood flow to the kidneys, which helps their kidneys and may even hide kidney disease"; after treatment "the blood flow to the kidneys returns to normal and the kidney function in some cats will worsen". "Older cats often have both hyperthyroidism and kidney disease, and treating these cats is a delicate balancing act." fda.gov Retrieved 2026-09-27.
- ASPCA. Which Lilies Are Toxic to Pets? — lilies of the genus "Lilium sp, are ones to keep your cats away from" and "Daylilies (Hemerocallis spp.) are also another lily to avoid." "All parts of the plant are toxic and small amounts can cause severe injury to the kidneys." "Drinking the water containing a lily or grooming pollen off their fur may cause problems as well." "However, it is often fatal if treatment is delayed longer than 18 hours after ingestion." "If you believe that your pet may have been exposed to or ingested something toxic please contact your veterinarian or ASPCA Poison Control at (888) 426-4435 immediately." aspca.org Retrieved 2026-09-27.
- Merck Veterinary Manual. Diabetes Mellitus in Dogs and Cats (Endocrine System) — "Some dogs and up to 50% of cats with diabetes mellitus have a decreased appetite." "The renal threshold for glucose (ie, the serum glucose concentration above which glucosuria develops) is approximately 180 mg/dL in dogs and approximately 280 mg/dL in cats." "Common clinical signs include the following: polyuria, polydipsia, polyphagia, weight loss, cataracts (dogs), weakness". merckvetmanual.com Retrieved 2026-09-27.