Serious severity

Glomerulonephritis

Inflammation of the kidney's tiny filtering units (glomeruli), which causes valuable protein to leak out into the urine and can lead to kidney damage.

⚠️ Common symptoms

Weight loss despite a normal appetiteIncreased thirst and urinationPoor coat condition and lethargySwelling of the limbs or belly in severe cases (fluid retention)Sometimes no obvious signs early on

Each kidney contains thousands of microscopic filters called glomeruli, whose job is to strain waste out of the blood while keeping useful substances such as protein inside the body. In glomerulonephritis these filters become inflamed and leaky, so protein that should stay in the bloodstream escapes into the urine.

The condition is usually a consequence of something else going on in the body. Often the immune system, reacting to a chronic infection, inflammation or a tumour, produces immune complexes that become trapped in the glomeruli and set off the damaging inflammation. For that reason, a thorough work-up looks not just at the kidneys but for an underlying trigger that can be treated.

Losing large amounts of protein has knock-on effects: cats may retain fluid, and they face a higher risk of abnormal blood clots. Managing the disease means slowing the protein leak and protecting kidney function with medication and diet, while addressing the root cause wherever it can be found. Caught early, before extensive scarring sets in, many cats can be stabilised for a good period.

🔍 Causes

Glomerulonephritis is usually driven by the immune system: immune complexes lodge in the delicate filters and inflame them. This is often secondary to another condition such as a chronic infection (including FeLV or FIV), inflammation elsewhere in the body, or certain cancers.

🛡 Prevention

Because it is often secondary, prevention centres on protecting overall health — keeping cats up to date on relevant vaccinations, preventing and promptly treating infections, and attending routine check-ups where urine screening can catch protein loss early.

💊 Treatment

Treatment targets both the kidney damage and any underlying trigger. Vets may prescribe medication to reduce protein loss and control blood pressure, a therapeutic kidney diet, and sometimes clot-preventing drugs because heavy protein loss raises clotting risk. Finding and treating the underlying infection, inflammation or tumour is a key part of management.

When to see a vet: See a vet if your cat is losing weight, drinking or urinating more, or seems generally unwell. Urine testing that reveals protein warrants further investigation before kidney function is lost.

⚕️ Medical disclaimer

  • This information is educational only and is not a substitute for veterinary advice.
  • Symptoms overlap between conditions — only a vet can diagnose accurately.
  • Never withhold treatment or self-medicate based on information found online.
  • When in doubt, call your vet. Early intervention almost always leads to better outcomes.

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