Chronic Kidney Disease in Cats: What the Stages Actually Mean

Chronic kidney disease (CKD) affects a substantial proportion of cats over the age of ten, and the kidneys' limited ability to regenerate means damage accumulates gradually and silently for years before bloodwork or symptoms change noticeably. By the time increased thirst or weight loss is obvious at home, a significant amount of kidney function has usually already been lost.

This is not a single disease with one cause — it is a description of long-term, irreversible kidney damage that can result from ageing, past infections, high blood pressure, certain toxins or genetic predisposition in some breeds. In most individual cats, no single cause is ever pinpointed.

Veterinarians commonly use the International Renal Interest Society (IRIS) system, which combines a blood marker (creatinine, and increasingly SDMA, which can rise earlier) with urine concentration and blood pressure to place a cat into one of four stages. Staging is not a one-off snapshot — vets look for a stable trend across repeated tests rather than reacting to a single result, since hydration and stress can shift values.

Earlier stages focus on slowing progression and managing any contributing factors such as high blood pressure or protein loss in the urine; later stages add management of the direct consequences of reduced kidney function, including nausea, appetite loss and anaemia.

A prescription renal diet, formulated with reduced and higher-quality protein and controlled phosphorus, is the single intervention most consistently linked to a longer and more comfortable life in cats with CKD, but only once a cat is reliably eating it — a diet a cat refuses provides no benefit at all. Fresh water availability, wet food to increase overall fluid intake, and treating any secondary hypertension or urinary tract infection promptly all support the kidneys that remain functioning.

Many cats do well for a long time with monitoring, diet and, where indicated, medications for blood pressure or phosphate binding. Decisions should always sit with your vet, since dosing and diet changes depend on the individual cat's bloodwork and body condition.

A cat with known CKD that stops eating entirely, becomes markedly lethargic, vomits repeatedly, or seems disoriented needs same-day veterinary assessment, since these can signal an acute worsening (sometimes called an 'acute on chronic' crisis) that may still be treatable with intensive support if caught early.