What is kidney disease in cats
Chronic kidney disease in cats is an incurable, progressive loss of kidney function that affects over half of cats over seven years old, causing weight loss, excessive thirst, and vomiting.
Chronic kidney disease (CKD) is an incurable, progressive loss of kidney function caused by inflammation of the renal tubules and interstitial tissue, affecting over half of cats by age seven. The disease is characterized by a gradual decrease in nephrons, leading to a failure to filter toxins and maintain fluid balance, with symptoms only becoming apparent after two-thirds of kidney function is already lost.
Why the disease remains hidden until late
Cats possess a massive renal reserve capacity, allowing the remaining healthy nephrons to compensate for damaged tissue for a long time. This physiological buffer means clinical symptoms do not appear until more than 66% of the original kidney function has been destroyed. Consequently, the disease often progresses silently for months or years, and by the time a cat shows signs of illness, the damage is already advanced. This delay is why CKD is frequently diagnosed in older cats, with over 50% of affected animals being seven years old or older.
The mechanism of toxin accumulation and vomiting
As the glomerular filtration rate drops, toxic metabolic byproducts like urea accumulate in the blood, a state known as uremia. This triggers vomiting through three distinct mechanisms: direct irritation of the chemoreceptor trigger zone in the brain, increased gastrin secretion leading to gastric hyperacidity, and vascular inflammation that damages the digestive tract lining. The resulting nausea and vomiting create a vicious cycle where the cat loses more fluid, exacerbating dehydration and further concentrating the toxins in the blood.
Electrolyte collapse and bone destruction
The failing kidneys cannot excrete phosphate efficiently, leading to hyperphosphatemia, while simultaneously failing to activate vitamin D3 (calcitriol), which causes a drop in blood calcium (hypocalcemia). In response, the parathyroid glands release excessive parathyroid hormone to compensate, a condition known as secondary renal hyperparathyroidism, which occurs in 84% of CKD cases. This hormone forces calcium and phosphate out of the bones to restore blood levels, leading to renal bone disorders and the calcification of soft tissues, including the kidneys, skin, heart, and blood vessels.
Fluid loss and blood pressure dysregulation
Loss of nephrons reduces the number of sodium ion channels, destroying the concentration gradient required for water reabsorption in the kidney tubules. This results in polyuria, where the cat produces excessive urine, leading to severe dehydration despite increased drinking (polydipsia). Furthermore, the kidney's ability to regulate blood pressure is impaired; autoregulation of renal blood flow fails, and the activation of the renin-angiotensin-aldosterone system often causes systemic hypertension. High blood pressure damages the delicate blood vessels in the eyes and further accelerates kidney destruction through pressure overload.
Stages, diet, and treatment limits
Diagnosis relies on blood creatinine levels to stage the disease, which is further subdivided by urine protein-creatinine quotients and blood pressure readings. While the disease is incurable, early intervention can slow progression and improve quality of life. Treatment focuses on reducing dietary protein and phosphate to match the cat's basic requirements, as cats have a unique metabolism that requires high animal protein but suffers from the high phosphate content in standard diets. Medications are used to manage secondary issues like metabolic acidosis, anemia, and electrolyte imbalances, but the underlying loss of functional kidney tissue is permanent.
Triggers and diagnostic limitations
While the primary cause is idiopathic tubulointerstitial nephritis, other factors can trigger renal dysfunction, including infections, autoimmune diseases, tumors, and exposure to toxins like lilies, ethylene glycol, or certain medications. Diagnosis involves palpation to check for kidney size and texture, blood pressure measurement, and imaging via X-ray or ultrasound to detect calcifications or structural changes. Although blood and urine tests are essential, the lack of sensitive diagnostic tools for early-stage disease means that by the time a definitive diagnosis is made, the cat has already lost a significant portion of its renal function.