Kidney failure in cats stems from two broad categories: sudden damage from toxins or infections, and gradual decline that builds over months or years. Chronic kidney disease is the more common form, affecting a significant proportion of cats over age 10, while acute kidney injury can strike cats of any age when they’re exposed to the wrong substance or develop a severe infection. Understanding which causes are preventable and which are not can help you protect your cat and catch problems early.
Chronic Kidney Disease: The Most Common Form
Most cases of kidney failure in cats develop slowly. The kidneys lose filtering capacity over time, and the body compensates well enough that you won’t notice anything wrong in the early stages. By the time symptoms appear, a substantial amount of kidney function has already been lost. This is why chronic kidney disease (CKD) is often diagnosed in older cats, typically those over 10.
The frustrating reality is that in many cats, no single cause can be identified. The kidneys simply wear down with age, and certain cats seem more vulnerable than others. Known contributing factors include:
- Genetic predisposition. Persian cats and Exotic Shorthairs are particularly at risk. A study of these breeds found polycystic kidney disease (PKD), a condition where fluid-filled cysts slowly replace healthy kidney tissue, in roughly 40% of Persians and 39% of Exotic Shorthairs. PKD is inherited, so if you have one of these breeds, early screening with ultrasound is worthwhile.
- Chronic infections. Bacterial kidney infections (pyelonephritis) are caused by bacteria, most commonly E. coli, that travel up from the lower urinary tract. These infections can smolder quietly, causing repeated damage that chips away at kidney function over time. Pyelonephritis is a recognized cause of acute-on-chronic kidney disease, meaning it can worsen already declining kidneys.
- High blood pressure. About 61% of cats with chronic kidney failure also have elevated blood pressure. It works both ways: kidney disease raises blood pressure, and high blood pressure damages the tiny blood vessels inside the kidneys, accelerating the decline. This creates a cycle that’s hard to break without treatment.
- Hyperthyroidism. An overactive thyroid gland is extremely common in older cats, and 87% of untreated hyperthyroid cats have elevated blood pressure. The excess thyroid hormone increases blood flow through the kidneys, which can temporarily mask kidney disease. Once hyperthyroidism is treated and blood flow normalizes, previously hidden kidney problems often become apparent. This doesn’t mean treatment caused the kidney disease; it was already there.
Toxic Substances That Cause Sudden Kidney Failure
Acute kidney injury happens fast, sometimes within hours of exposure to a toxic substance. Unlike chronic disease, this type of kidney failure can affect young, otherwise healthy cats. The good news is that most of these causes are preventable.
Lilies
Lilies are the single most dangerous household plant for cats. Every part of the plant, including petals, leaves, pollen, and even the water in the vase, contains a chemical that destroys kidney cells. A cat that chews on a single leaf or gets pollen on its fur and licks it off can develop life-threatening kidney failure. The treatment window is narrow: delayed treatment beyond 18 hours after ingestion generally leads to irreversible damage. If you have cats, the safest approach is to never bring lilies into your home. This applies to true lilies in the Lilium genus (Easter lilies, tiger lilies, Asiatic lilies) and daylilies.
Antifreeze
Ethylene glycol, the main ingredient in most automotive antifreeze, has a sweet taste that attracts cats. Even a small amount causes crystals to form inside the kidneys, blocking their ability to filter blood. Kidney failure from antifreeze progresses rapidly, and survival depends on treatment within the first few hours. Keep antifreeze containers sealed and clean up any spills immediately, including puddles under parked cars.
Human Pain Medications
Common over-the-counter painkillers like aspirin, ibuprofen, and acetaminophen (Tylenol) are all toxic to cats. Cats lack the liver enzymes needed to process these drugs safely, and their kidneys bear much of the damage. A single pill can be enough to cause serious harm. Never give your cat human medication unless specifically directed by a veterinarian.
Infections That Damage the Kidneys
Beyond chronic low-grade infections, acute bacterial kidney infections can cause sudden kidney injury. Bacteria from a bladder infection can travel upward into one or both kidneys, triggering inflammation and rapid tissue damage. Cats with urinary tract abnormalities or weakened immune systems are more vulnerable.
Fungal infections are less common but possible. Candida species are the most frequent culprits in urinary fungal infections, and the kidneys can also become involved during systemic fungal infections that spread through the bloodstream. These are rare compared to bacterial causes but tend to be more difficult to treat.
Early Signs You Might Notice
One of the reasons kidney disease is so dangerous in cats is that the early stages are silent. Cats are remarkably good at compensating for declining kidney function, and their body adjusts to maintain normal blood chemistry until roughly 65 to 75% of kidney capacity is gone.
The earliest change you’re likely to notice at home is increased water intake and larger volumes of urine. As the kidneys lose their ability to concentrate urine effectively, your cat drinks more to make up for the extra fluid loss. You might find yourself refilling the water bowl more often or noticing heavier clumps in the litter box. At this stage, your cat may still seem perfectly healthy otherwise.
As the disease progresses, waste products build up in the bloodstream because the kidneys can no longer clear them. This is when cats start to feel genuinely sick. They lose their appetite, lose weight, and their coat may look dull or unkempt. Lethargy, vomiting, and bad breath (from waste products accumulating in the blood) are common in more advanced stages. The loss of important proteins and vitamins through poorly functioning kidneys contributes to the metabolic disruption that makes cats feel unwell.
How Kidney Failure Is Detected
Because early symptoms are so subtle, routine bloodwork is the most reliable way to catch kidney disease before it becomes advanced. Veterinarians use two key blood markers to assess kidney function. One is creatinine, a waste product that rises as kidney filtration declines. The other is SDMA, a newer and more sensitive marker. SDMA levels above 14 can indicate early kidney disease even when creatinine is still in the normal range, making it useful for catching CKD at a stage when intervention can slow the progression.
Urine concentration is another important clue. One of the earliest laboratory indicators of kidney disease in cats is dilute urine, meaning the kidneys aren’t pulling water back into the body efficiently. A routine urinalysis can flag this problem before blood values change significantly. For cats over 7 or 8, annual bloodwork and urinalysis give you the best chance of catching kidney disease early enough to make a difference in how long and how well your cat lives with the condition.
Why Some Cats Are More Vulnerable
Age is the single biggest risk factor for chronic kidney disease. The kidneys accumulate damage over a lifetime, and older cats are also more likely to have concurrent conditions like hyperthyroidism or high blood pressure that compound the problem. Certain breeds carry genetic risks: Persians and Exotic Shorthairs with their high rates of PKD, but also breeds like Abyssinians and Siamese, which some veterinary sources consider predisposed to kidney issues.
Cats that have survived an episode of acute kidney injury, even if they recovered fully, may have reduced kidney reserve that makes them more susceptible to chronic disease later in life. Repeated urinary tract infections, long-term exposure to a kidney-unfriendly diet (very high in phosphorus, for instance), and chronic dehydration from a dry-food-only diet without adequate water intake can all contribute to gradual kidney wear over the years.