By Dr Duncan Houston
Finding protein in your cat’s urine can be the first clue that the kidneys need closer investigation. It does not, by itself, prove that the kidney filters are inflamed.
Glomerulonephritis is one cause of protein loss through the kidneys. Establishing the source and severity matters because the treatment can be very different from treatment for a urinary infection.
Quick Answer
Glomerulonephritis is inflammation affecting the kidney’s microscopic filters. It can cause persistent protein loss, high blood pressure and progressive kidney injury. Diagnosis requires more than a urine dipstick, and treatment is tailored to kidney function, blood pressure, protein loss and the underlying disease.
What makes this different from other kidney disease?
The glomeruli filter blood while normally retaining larger proteins. Injury can allow excessive protein, including albumin, to escape into urine. Marked albumin loss can contribute to fluid accumulation and clotting complications.
Cats can have renal protein loss for reasons other than glomerulonephritis. A study of feline protein-losing kidney disease shows the importance of distinguishing specific tissue diagnoses rather than treating every protein-positive sample as the same condition.
Which tests help?
A urine sediment examination and, when indicated, culture help exclude inflammation, blood or infection lower in the urinary tract. Persistent renal protein loss is measured with the urine protein-to-creatinine ratio. Blood tests assess kidney markers, albumin and other changes; blood pressure is checked separately.
Repeat measurements establish a pattern. Ultrasound can assess kidney structure but cannot identify every microscopic disease. A kidney biopsy may be considered when the likely benefit of a specific diagnosis justifies its risks.
How is treatment chosen?
Care may include treatment of a verified underlying infection or inflammatory condition, appropriate kidney nutrition, blood-pressure control and medication to reduce protein loss. Hydration and kidney values need monitoring when these medicines are started or changed.
Immunosuppressive drugs are not an automatic response to protein in urine. They require a strong rationale, often with specialist input and biopsy information. Clot-prevention decisions are also individual; do not give aspirin yourself. IRIS guidance on proteinuria supports confirming persistent renal protein loss and following its course.
How worried should you be?
| What you notice | Why it matters | What to do |
|---|---|---|
| Protein found on a routine sample, otherwise well | Needs confirmation and localisation | Arrange the recommended urine and blood-pressure follow-up. |
| Weight loss, increasing thirst, vomiting or swelling | Possible clinically significant kidney or protein loss | Contact your vet today. |
| Sudden blindness, breathing difficulty, collapse or painful paralysis | Potential hypertensive or clotting complication | Seek emergency care now. |
What else could explain these signs?
Urinary tract inflammation, infection, blood contamination, chronic kidney disease without glomerulonephritis and other glomerular conditions can all cause protein-positive results. Increased thirst alone also has several non-kidney causes.
When is this an emergency?
Sudden loss of vision, seizures, severe weakness, breathing difficulty or a suddenly painful weak limb needs emergency assessment. Repeated vomiting, inability to keep water down or markedly reduced urine production also needs urgent attention.
What should you do next?
- Bring previous laboratory results so the vet can compare trends.
- Record eating, drinking, urination, weight and any swelling.
- Give prescribed medicines consistently and attend scheduled blood, urine and blood-pressure checks.
- Ask before introducing supplements, anti-inflammatory medicines or a major diet change. Never restrict access to water.
Common mistakes to avoid
- Diagnosing glomerulonephritis from one dipstick result.
- Starting steroids without establishing the likely cause.
- Using aspirin or human painkillers for presumed clots or discomfort.
- Assuming normal kidney blood markers rule out important protein loss.
Prevention and ongoing care
There is no reliable home method to prevent every glomerular disease. Routine health checks and investigation of persistent proteinuria can identify problems before severe signs develop.
Maintain an appropriate body condition and follow the nutritional plan without allowing a prescribed diet transition to result in prolonged poor intake.
Frequently asked questions
Does protein in urine always mean kidney failure?
No. The source, persistence and amount of protein must be interpreted alongside other findings.
Can glomerulonephritis be cured?
Some underlying causes can be treated, but established kidney damage may require long-term management.
Does every cat need a kidney biopsy?
No. It is considered when its result would change care and the benefits outweigh the risks.
Are steroids always needed?
No. Unselected immunosuppression can be unhelpful or harmful, especially if infection is present.
The useful next step is to confirm where the protein is coming from and how much it matters. A measured treatment and monitoring plan is safer than treating a laboratory label alone.
For more practical animal health information, explore ASK A VET™. If your animal has emergency signs, contact a veterinary clinic immediately.
The ASK A VET™ Tracker logs live location and activity trends, so a change in routine never goes unnoticed.
- Cats
- Glomerulonephritis
- Kidney Health
- Pet Health
Every ASK A VET article is written and reviewed by qualified veterinarians.
