The bottom line first: if your cat has started drinking noticeably more, the urine clumps have grown, and the weight is slowly dropping, get the kidneys checked regardless of age. By the time it's obvious from the outside, the disease is often well advanced.
Chronic kidney disease (CKD, often called "kidney failure") is one of the most common conditions of older cats. Across all cats it affects only a small percentage, but the numbers climb steeply with age — as many as 30% to 50% of cats older than 15 have been reported to have CKD. The kidneys filter waste and keep water and electrolytes in balance, and once that tissue is damaged it does not grow back. So the goal here is not a cure but slowing the disease down, and how well that goes depends heavily on how early it was caught.
The kidneys have a large reserve. By the time standard blood values (creatinine, BUN) start to rise, roughly 75% of functioning nephrons are already gone. In other words, "the values are normal, so we're fine" is not much reassurance in the early stages. On top of that, cats hide illness well, and the first changes are easy to write off as "just getting older."
The most practical thing you can do is track weight and water intake. Weigh your cat monthly on the same scale and keep a rough idea of how much water you pour into the bowl — changes show up far sooner that way. To set a baseline for how much your cat should be drinking, try our daily water intake calculator. If you're curious where your cat sits in human years, the cat age calculator is there too.
The foundation is blood work and a urine test together. A drop in the ability to concentrate urine (urine specific gravity) often appears before blood values change, so skipping the urine test makes it easy to miss the earliest signal. SDMA is now widely used as well: in one study, SDMA rose above the reference range a median of about 17 months before creatinine did in cats that went on to develop azotemic CKD. Add blood pressure measurement and ultrasound, and the case is staged 1 to 4 under the International Renal Interest Society (IRIS) system, which then guides management. Which tests to run, how often, and how to read the results varies from cat to cat, so an accurate diagnosis requires a veterinary consultation.
As for screening, once-a-year checks from around age 7–8 and every six months from age 10 are commonly recommended. What matters most is building a baseline for your own cat while they're healthy — the same number means something different depending on whether it has risen from that cat's normal.
The first is hydration. Kidneys that can't concentrate urine let the body dry out quickly, so leaning more on wet food and placing water bowls around the home both help. Be extra careful in summer, when dehydration comes on faster. The second is diet: renal diets with controlled phosphorus and protein have evidence behind them for extending survival. When to switch and to which formula depends on the stage, so decide it with your vet. The third is managing what comes with it — high blood pressure, rising phosphorus, low potassium, anemia and protein loss in the urine often accompany CKD, and each of them damages the kidneys faster. That's why regular rechecks are part of the treatment, not an optional extra.
There are also things not to try on your own. Human anti-inflammatory painkillers (ibuprofen and the like) are dangerous for cats, and unproven supplements or human foods billed as "good for the kidneys" can add a phosphorus or sodium load. Ask your vet before changing what goes in the bowl.
Kidney tissue lost to chronic kidney disease cannot be restored. What is very possible is slowing the progression and easing the symptoms, and cats that are found early and managed from that point tend to do better. That is exactly why early diagnosis matters.
No. Diabetes, hyperthyroidism and pyometra are other common causes of increased thirst, and the reason can also be as simple as hot weather or a dry-food-only diet. Still, if the increase is clear and lasts more than a few days, blood and urine tests are needed to tell the causes apart.
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This content is general information and does not replace veterinary diagnosis. For an accurate diagnosis and treatment, always consult a veterinarian.