Chronic kidney disease (CKD) is a gradual, permanent loss of kidney function that affects roughly 30 to 40 percent of cats over the age of 10. The kidneys slowly lose their ability to filter waste from the blood and concentrate urine, and because the damage accumulates over months or years, many cats show no obvious symptoms until significant function is already gone. It’s one of the most common diagnoses in older cats and a leading cause of death in senior felines.
What the Kidneys Do and What Goes Wrong
A cat’s kidneys contain hundreds of thousands of tiny filtering units called nephrons. Each nephron removes waste products from the blood, regulates electrolyte levels, and helps control blood pressure. In CKD, nephrons are gradually destroyed and replaced by scar tissue. Unlike some organs, the kidneys cannot regenerate these units once they’re lost.
The remaining healthy nephrons compensate by working harder, which keeps blood values looking normal for a surprisingly long time. This is why CKD often isn’t detected until 65 to 75 percent of total kidney function has been lost. One of the earliest measurable changes is that the kidneys lose the ability to concentrate urine effectively. Cats begin producing large volumes of dilute urine and drinking more water to compensate. This increased thirst and urination is often the first thing owners notice.
Common Causes and Risk Factors
In most cats, no single cause is identified. The disease is strongly associated with aging, and the cumulative wear on kidney tissue over a lifetime appears to be the primary driver. Certain breeds, particularly Persians and related breeds, carry a genetic risk for polycystic kidney disease, a condition where fluid-filled cysts gradually replace functional kidney tissue.
Other known contributors include chronic urinary tract infections, kidney stones, and exposure to toxins (certain plants, antifreeze, or prolonged use of some medications). High blood pressure and hyperthyroidism, both common in older cats, can also accelerate kidney damage. Dental disease has been investigated as a possible contributor, since chronic oral bacteria can enter the bloodstream and stress the kidneys, though this link is still debated.
Signs to Watch For
Early CKD is subtle. Your cat may drink slightly more water than usual or visit the litter box more often. Because these changes happen gradually, they’re easy to miss. As the disease progresses, more noticeable signs develop:
- Increased thirst and urination: The hallmark early sign. You may notice the water bowl emptying faster or litter clumps becoming larger and more frequent.
- Weight loss: Often gradual, sometimes dramatic. Muscle wasting along the spine and hips is common.
- Decreased appetite: Waste products building up in the blood cause nausea, making cats eat less or become picky about food.
- Vomiting: Linked to the buildup of toxins the kidneys can no longer clear.
- Poor coat quality: The fur may look dull, unkempt, or greasy.
- Lethargy: Less interest in play, more sleeping, general withdrawal.
- Bad breath: A metallic or ammonia-like odor can develop as waste products accumulate.
In advanced stages, cats can develop mouth ulcers, severe dehydration, seizures, and a dangerous drop in body temperature.
How CKD Is Diagnosed
Diagnosis relies on blood work and a urine sample. Your vet looks at two key blood markers: creatinine and SDMA. Both are waste products that rise when the kidneys aren’t filtering properly. SDMA is considered the more sensitive test because it can detect reduced kidney function earlier than creatinine alone. A normal SDMA level is 14 micrograms per deciliter or below in cats; persistent values above this suggest kidney disease.
The urine test measures how well the kidneys concentrate urine. A low urine specific gravity, meaning the urine is overly dilute, is one of the earliest indicators of CKD and sometimes shows up before blood values become abnormal. Blood pressure measurement and a complete blood count to check for anemia round out the picture.
The Four Stages of CKD
Veterinarians use the International Renal Interest Society (IRIS) staging system to classify CKD into four stages based on blood creatinine and SDMA levels. Staging matters because it guides treatment decisions and gives you a general sense of prognosis.
- Stage 1: Blood values are normal or only mildly elevated (SDMA around 15 to 17). Kidney damage exists but the body is still compensating well. Most cats have no visible symptoms.
- Stage 2: Mild kidney insufficiency. SDMA persistently above 17, creatinine mildly elevated. Increased thirst and urination may become noticeable. Cats generally feel well at this stage.
- Stage 3: Moderate kidney failure. Waste products are accumulating enough to cause clinical signs like appetite loss, nausea, and weight loss. This is the stage where many cats are first diagnosed.
- Stage 4: Severe kidney failure. Blood values are markedly elevated and cats are typically quite ill, with significant nausea, weakness, and dehydration.
Substaging also considers blood pressure and protein levels in the urine, both of which influence how aggressively the disease is managed.
Complications That Can Develop
CKD doesn’t just affect the kidneys. As the disease progresses, it creates a cascade of problems throughout the body.
High blood pressure is common in cats with CKD and can damage the eyes, brain, and heart. Some cats experience sudden blindness from retinal detachment caused by uncontrolled hypertension. Regular blood pressure checks become part of routine monitoring once CKD is diagnosed.
Anemia develops because healthy kidneys produce a hormone that stimulates red blood cell production. As kidney tissue is lost, this hormone drops, leaving cats with fewer red blood cells. The result is fatigue, weakness, and pale gums. Elevated phosphorus is another frequent complication. When the kidneys can’t excrete phosphorus effectively, it accumulates in the blood and accelerates further kidney damage, creating a vicious cycle.
How CKD Is Managed
There is no cure for CKD. The goal of treatment is to slow progression, manage symptoms, and maintain quality of life for as long as possible. What that looks like depends heavily on the stage at diagnosis.
Diet Changes
Therapeutic kidney diets are one of the most impactful interventions. These foods are restricted in both protein and phosphorus compared to regular cat food. Phosphorus levels in renal diets are typically held around 0.5 percent, which is significantly lower than standard maintenance foods. Protein is also reduced, with therapeutic options ranging from roughly 26 to 37 percent depending on the formulation. Studies have shown that cats fed prescription renal diets live longer and have fewer uremic symptoms than those on regular food. The challenge is getting cats to eat them, since many are picky eaters, especially when nausea is involved.
Hydration Support
Because CKD cats lose excessive water through dilute urine, keeping them hydrated is critical. Switching from dry food to wet food helps. Water fountains encourage some cats to drink more. For cats with moderate to advanced disease, many owners learn to give subcutaneous fluids at home. This involves injecting a balanced electrolyte solution under the skin, typically at doses of 10 to 30 milliliters per kilogram of body weight, a few times per week. Most cats tolerate this well, and it can significantly improve how they feel.
Medications and Supplements
Depending on the complications present, your vet may recommend phosphorus binders mixed into food, medications to control blood pressure, appetite stimulants, or anti-nausea medications. Potassium supplements are common because CKD cats tend to lose potassium through their urine, leading to muscle weakness.
What to Expect Over Time
CKD is progressive, but the speed of progression varies enormously between cats. Some cats diagnosed at Stage 2 live comfortably for several years with dietary management and monitoring alone. Others progress more quickly, particularly if complications like uncontrolled high blood pressure or persistent high phosphorus develop.
Cats diagnosed at Stage 1 or 2 generally have the best outlook, with many living two to three years or longer after diagnosis. Stage 3 cats often do well for months to over a year with active management. Stage 4 carries the most guarded prognosis, though even at this stage, some cats stabilize enough to enjoy additional weeks or months of good quality life with supportive care.
Regular monitoring is essential regardless of stage. Most vets recommend rechecking blood work and urine every three to six months for early-stage disease, and more frequently as the disease advances. These check-ins catch complications early and allow treatment adjustments before your cat feels significantly worse. The single most important factor in long-term outcomes is catching the disease early, which is why routine blood work in cats over seven or eight years old is so valuable.