Understanding Chronic Kidney Disease in Cats
Chronic Kidney Disease, commonly abbreviated to CKD, is one of the most frequently diagnosed conditions in older cats. Studies suggest that a significant proportion of cats over the age of ten have some degree of kidney dysfunction, making it one of the leading causes of illness and death in senior felines. The good news is that with early detection and careful management, many cats with CKD can continue to enjoy a good quality of life for months or even years after diagnosis.
The kidneys perform a wide range of vital functions: filtering waste products from the blood, regulating fluid and electrolyte balance, controlling blood pressure, and producing hormones that stimulate red blood cell production. When kidney function declines, all of these processes are gradually impaired.
The IRIS Staging System
The International Renal Interest Society (IRIS) has developed a widely used staging system for CKD in cats that helps vets assess severity and guide treatment. The system is based primarily on two blood markers: creatinine and SDMA (symmetric dimethylarginine).
Stage 1
At Stage 1, creatinine levels are within the normal range but SDMA may already be elevated, or there may be other signs of kidney damage such as protein in the urine. The cat may have no obvious symptoms at all at this stage. Stage 1 represents the earliest detectable form of CKD.
Stage 2
Stage 2 involves mildly elevated creatinine levels. Cats may begin drinking slightly more water than usual and urinating more frequently, but many owners do not notice these subtle changes, or attribute them to normal variation. This is often the stage at which CKD is first identified during routine blood testing.
Stage 3
At Stage 3, creatinine is moderately elevated and kidney function is significantly reduced. Symptoms become more noticeable: increased thirst and urination, weight loss, reduced appetite, and occasional vomiting. Blood pressure may also be elevated at this stage, requiring treatment.
Stage 4
Stage 4 represents severe kidney failure. Creatinine levels are markedly elevated, and the cat's kidneys are functioning at a very low capacity. Symptoms include profound weight loss, poor appetite or complete inappetence, vomiting, lethargy, and potentially mouth ulcers caused by the build-up of urea in the bloodstream — a condition called uraemia. Anaemia is also common at this advanced stage. Palliative care and quality of life become the central concerns.
SDMA: An Early Warning Biomarker
SDMA is an important biomarker that can detect significant kidney dysfunction earlier than creatinine. Research has shown that SDMA begins to rise when kidney function has declined by approximately 40 percent, whereas creatinine does not typically rise until around 75 percent of function has been lost. This earlier detection window gives owners and vets more time to intervene with management strategies before the disease has progressed as far. Many vets now include SDMA as a routine part of senior cat health screening, and IRIS staging incorporates SDMA alongside creatinine for more accurate classification.
Managing CKD: Phosphorus Restriction
One of the most evidence-based interventions in CKD management is phosphorus restriction. Damaged kidneys are less able to excrete phosphorus, which then builds up in the bloodstream and accelerates further kidney damage. Reducing dietary phosphorus is therefore one of the most important things an owner can do to slow disease progression.
Purpose-formulated renal diets are designed with reduced phosphorus and protein levels and are the cornerstone of dietary management in CKD. They are available as both wet and dry food options. Transitioning a cat to a renal diet gradually is important, as a sudden change can put a cat off its food entirely — not ideal for an already fragile patient. For cats whose phosphorus remains elevated despite a renal diet, phosphate binders can be added to food to reduce absorption from the gut.
Subcutaneous Fluid Therapy at Home
As CKD progresses, cats often become chronically dehydrated because their damaged kidneys are no longer able to concentrate urine effectively. Subcutaneous (under the skin) fluid therapy involves administering a small volume of sterile saline or lactated Ringer's solution under the skin, typically over the scruff of the neck. This provides additional hydration that supplements what the cat drinks.
Many owners successfully learn to administer subcutaneous fluids at home under veterinary guidance. The technique involves using a needle attached to a giving set and a bag of fluids, gently tenting the skin and inserting the needle. Most cats tolerate it well, and some even appear to feel noticeably better shortly after their fluids. Your vet will guide you on frequency and volume based on your cat's individual needs.
Medications Used in CKD Management
Appetite Stimulants
Maintaining food intake is critical in CKD, as weight loss accelerates decline. Mirtazapine is a commonly used appetite stimulant available as a transdermal gel applied to the inner ear flap. Capromorelin (sold as Elura in some markets) is a newer appetite stimulant specifically licensed for use in cats with CKD.
Semintra for Proteinuria and Hypertension
Semintra, containing the active ingredient telmisartan, is licensed specifically for the management of proteinuria (protein in the urine) and hypertension in cats with CKD. Both proteinuria and high blood pressure independently accelerate kidney damage, so controlling them is an important part of slowing disease progression. Semintra is administered orally as a liquid and is generally well tolerated.
Managing Anaemia
The kidneys produce a hormone called erythropoietin, which stimulates the bone marrow to produce red blood cells. In advanced CKD this production is impaired, leading to anaemia. Darbepoetin is an injectable drug that mimics erythropoietin and can improve red blood cell counts in affected cats. It is typically administered by the vet or by owners trained to give injections at home.
Palliative Care and Quality of Life
As CKD reaches its advanced stages, the focus shifts from slowing progression to maintaining comfort and quality of life. Ensuring your cat is eating, comfortable, and enjoying its daily life becomes the priority. Many vets use structured quality of life assessment tools to help owners evaluate how their cat is doing.
Knowing when the time is right to say goodbye is one of the most difficult decisions any cat owner faces. The key questions centre on whether your cat is experiencing more good days than bad, whether they are still engaging with food, company, and their environment, and whether their suffering can be effectively managed. Your vet is your most important partner in this conversation, and there is no shame in asking for honest guidance when the time comes.