The Kidneys and Why They Matter So Much in Older Cats
Chronic kidney disease is the most common cause of death in domestic cats over the age of ten. Studies suggest it affects between 30 and 40 percent of cats aged fifteen and above. Despite this prevalence, it frequently goes undetected until a substantial portion of kidney function has already been lost — a consequence of both the gradual nature of its progression and the fact that cats rarely display obvious signs of illness until disease is well established.
The kidneys perform several vital functions: filtering waste products from the blood, regulating fluid and electrolyte balance, producing hormones involved in red blood cell production, and maintaining blood pressure. When kidney function declines significantly, the consequences ripple through almost every system in the body.
Why Early Detection Is So Difficult
The kidneys have enormous reserve capacity. A cat does not typically show clinical signs of kidney disease until approximately 75 percent of kidney function has been lost. This means that by the time a cat appears unwell, the disease is already in an advanced stage. Traditional blood tests — specifically creatinine measurements — do not begin to elevate outside the normal range until this same threshold is crossed.
This diagnostic gap led to the development of a biomarker called symmetric dimethylarginine, or SDMA, which becomes elevated much earlier in the disease process — when kidney function has declined by as little as 25 percent. Routine SDMA testing in senior cats is increasingly recommended as standard practice and can provide a two to four year earlier diagnosis compared to creatinine alone.
Recognising the Signs
By the time clinical signs appear, they are often unmistakable once you know what to look for:
- Increased thirst and urination — the kidneys lose their ability to concentrate urine, producing larger volumes of dilute urine
- Weight loss and muscle wasting, often despite a reasonable appetite initially
- Reduced appetite progressing to food refusal in later stages
- Vomiting, particularly in the mornings or when the stomach is empty
- A dull, unkempt coat from reduced grooming
- Lethargy and reduced activity
- Bad breath with an ammonia-like or metallic quality
- Mouth ulcers in more advanced disease
Increased thirst and urination are often the earliest signs owners notice, and they should always prompt a veterinary investigation in a cat over seven.
Staging Chronic Kidney Disease
The International Renal Interest Society has developed a widely used staging system for feline chronic kidney disease based on creatinine levels and SDMA values. Stages run from one — where kidney damage is present but function is near normal — through to four, where disease is severe. Staging guides treatment decisions and helps predict prognosis. Blood pressure assessment and urine protein measurement are also incorporated into clinical decision-making.
Dietary Management: The Most Important Intervention
Nutrition is the cornerstone of chronic kidney disease management in cats. Phosphorus restriction is the most critical dietary modification. Excess dietary phosphorus accelerates kidney damage by causing mineral deposits within kidney tissue. Prescription kidney diets are formulated with reduced phosphorus and have been shown in clinical trials to extend life and improve quality of life in cats with kidney disease.
These diets also typically contain controlled protein levels. This is an area of ongoing research — cats are obligate carnivores with high protein requirements, and excessive protein restriction can worsen muscle wasting. The current consensus is that moderate protein restriction is appropriate in stages three and four, while cats in earlier stages may do better on protein levels closer to normal, adjusted based on urine protein measurements.
Hydration is crucial. Wet food should form the majority — ideally all — of the diet, as it significantly increases fluid intake. In cats with poor appetites, warming food gently can increase palatability. Phosphate binders added to food can further reduce phosphorus absorption and are used when dietary restriction alone is insufficient.
Medical Management
Several medical interventions complement dietary management. High blood pressure — common in cats with kidney disease — is treated with anti-hypertensive medications, most commonly amlodipine. Uncontrolled hypertension causes further kidney damage and can result in sudden blindness from retinal detachment.
Potassium supplementation is often needed, as the kidneys of affected cats excrete potassium inefficiently. Low potassium causes muscle weakness and contributes to further kidney deterioration. Anti-nausea medications improve appetite and quality of life. In some cats, regular subcutaneous fluid administration — given at home by owners using a technique taught by their vet — significantly supports hydration and slows disease progression.
Monitoring and Follow-Up
Cats with chronic kidney disease require more frequent veterinary monitoring than healthy cats. In early stages, six-monthly blood and urine checks are typical. In more advanced disease, monitoring every two to three months allows for timely adjustment of treatment. Blood pressure should be measured at every appointment.
Home monitoring can include regular weight checks, observation of food and water intake, and noting litter box habits. A sudden decrease in appetite, vomiting episodes, or a marked change in behaviour should prompt a veterinary contact ahead of the next scheduled appointment.
Quality of Life Considerations
A diagnosis of chronic kidney disease is not a death sentence, and it should not be treated as one. Cats in early to middle stages of the disease can live comfortably for years with appropriate management. The goal is not simply to extend life, but to ensure the life being lived is genuinely good — free from nausea, well-hydrated, well-nourished, and comfortable.
Working closely with a veterinarian who understands feline kidney disease and is committed to regular monitoring gives your cat the best chance of a long, well-managed life after diagnosis.