Testing for kidney disease in cats involves a combination of blood work, urinalysis, and sometimes imaging. No single test gives the full picture, so veterinarians use several together to confirm a diagnosis, determine how advanced the disease is, and track it over time. Because cats are skilled at hiding illness, routine screening starting around age 7 is the most reliable way to catch kidney problems early.
Blood Tests: SDMA and Creatinine
Blood work is the backbone of kidney disease testing in cats. Two key markers tell your vet how well the kidneys are filtering waste: creatinine and a newer marker called SDMA. These measure slightly different things, and using both together gives a more complete picture.
Creatinine has been the standard kidney marker for decades, but it has a major limitation. Levels don’t rise above normal until roughly 75% of kidney function is already gone. That means a cat can have significant kidney damage and still show normal creatinine on a blood panel. Creatinine is also influenced by muscle mass, hydration, and diet, which can make results less reliable in thin or dehydrated cats.
SDMA is more sensitive. It rises when a cat has lost an average of about 24% of kidney function, catching disease much earlier than creatinine alone. The normal upper limit for SDMA in cats is 14 µg/dl. A persistent reading of 15 to 17 places a cat in Stage 1 of chronic kidney disease under the International Renal Interest Society (IRIS) staging system, even if creatinine is still normal. Stage 2 is identified when SDMA exceeds 17 or creatinine rises above 2.7 mg/dl. Stages 3 and 4 reflect progressively higher values and more advanced loss of function.
Your vet will likely run a complete chemistry panel alongside these markers, checking for electrolyte imbalances, phosphorus levels, and other changes that help guide treatment decisions.
Urinalysis: What Your Cat’s Urine Reveals
A urine sample provides information that blood work alone cannot. The most important measurement is urine specific gravity, which tells your vet how well the kidneys are concentrating urine. Healthy cat kidneys produce concentrated urine with a specific gravity of at least 1.035. When the kidneys are damaged, they lose the ability to concentrate urine, and the specific gravity drops. A cat with elevated kidney values on blood work and dilute urine (below 1.035) has clear evidence of impaired kidney function.
The other critical urine measurement is the protein-to-creatinine ratio, or UPC. Healthy kidneys keep protein out of the urine, so finding protein there signals damage to the kidney’s filtering units. Cats are classified as non-proteinuric with a UPC below 0.2, borderline between 0.2 and 0.4, and proteinuric above 0.4. Proteinuria doesn’t just confirm kidney disease; it also worsens the prognosis. Cats spilling protein into their urine tend to progress faster, so this number helps your vet decide how aggressively to manage the condition.
A complete urinalysis also checks for bacteria, crystals, blood cells, and other abnormalities that could point to infection or urinary stones rather than (or in addition to) chronic kidney disease.
How to Collect a Urine Sample at Home
Your vet may ask you to bring in a urine sample, and collecting one from a cat is easier than it sounds. The key is replacing your cat’s regular litter with a non-absorbent alternative so the urine pools at the bottom of the tray instead of being soaked up. Pet supply stores sell non-absorbent litter designed specifically for this purpose. Shredded magazine paper also works in a pinch, since the glossy coating resists absorption better than newspaper.
Start by emptying, cleaning, and thoroughly drying the litter tray. Even traces of water or cleaning product can contaminate the sample. Sprinkle in the non-absorbent litter, place the tray in its usual spot, and wait. If your cat has outdoor access, you may need to temporarily block the cat flap so they use the tray instead. Check frequently, and if your cat passes stool, remove it immediately to keep the urine clean. Once your cat has urinated, tilt the tray to pool the liquid in one corner, draw it up with a syringe or dropper, and transfer it to a sample container. Label it with your name, your cat’s name, and the date and time. Deliver it to the vet as soon as possible. If you can’t go right away, store it in the fridge, but the sooner it’s tested the more accurate the results will be.
Some vets prefer to collect urine themselves via a method called cystocentesis, where a needle draws urine directly from the bladder. This gives the cleanest possible sample and is standard when testing for urinary tract infections.
Imaging: Ultrasound and X-Rays
Blood work and urinalysis confirm that the kidneys aren’t functioning properly, but imaging helps explain why. Ultrasound is generally more informative for kidney evaluation because it can reveal structural changes within the kidney tissue itself, including signs of infection (pyelonephritis), fluid buildup in the renal pelvis, cysts, and areas of tissue damage from reduced blood flow. These details allow your vet to tailor treatment to the specific underlying problem.
X-rays are better at detecting kidney stones and mineral deposits, which actually show up more reliably on radiographs than on ultrasound. X-rays also give a quick read on overall kidney size. Small, irregular kidneys on an X-ray are a classic sign of chronic kidney disease. In practice, many vets use both tools together when the situation calls for it.
Blood Pressure Measurement
High blood pressure and kidney disease are closely linked in cats. Damaged kidneys can drive blood pressure up, and high blood pressure can further damage the kidneys. The IRIS guidelines recommend measuring blood pressure in all cats diagnosed with kidney disease and substaging them based on the results. Systolic blood pressure consistently above 160 mmHg is considered hypertensive and typically warrants treatment to protect the eyes, brain, heart, and kidneys from further damage.
Even in apparently healthy older cats, high blood pressure is surprisingly common. One study found a prevalence of nearly 13% in cats aged 10 and older. Because of this, annual blood pressure checks are recommended for all senior and geriatric cats regardless of whether kidney disease has been diagnosed.
When and How Often to Screen
The American Association of Feline Practitioners classifies cats as “mature” at 7 to 10 years, “senior” at 11 to 14, and “geriatric” at 15 and older. Their guidelines recommend starting a baseline screening panel (blood work plus urinalysis) at age 7 to 10, with the frequency increasing as cats age. Apparently healthy senior cats should see the vet every six months, and a full diagnostic workup should be performed at least annually.
Early screening matters because kidney disease in cats is often silent in its early stages. The most recognizable symptoms, increased thirst and urination, tend to appear only after significant kidney function has been lost. Other signs like weight loss, decreased appetite, vomiting, and poor coat quality develop gradually and are easy to attribute to normal aging. By the time these changes are obvious, the disease may already be at Stage 2 or 3. Routine screening with SDMA-inclusive blood panels catches the problem months to years earlier, giving you more time to slow its progression with dietary changes, hydration support, and other interventions.
Putting the Results Together
No single test result defines kidney disease in cats. A diagnosis requires putting multiple pieces together: elevated SDMA or creatinine on blood work, dilute urine on urinalysis, protein loss in the urine, and sometimes structural changes on imaging. The IRIS staging system combines all of these data points to assign a stage (1 through 4) and substages based on proteinuria and blood pressure. This standardized framework helps your vet create a treatment plan matched to the severity of disease and gives you a baseline to track changes over time.
If your cat is over 7 and hasn’t had blood work and a urinalysis recently, a routine wellness panel is the simplest first step. It’s a quick, low-stress visit that can reveal problems long before your cat shows any outward signs of illness.