Glomerulonephritis in Dogs and Cats: What Protein in Urine Means
In this article
By Dr Duncan Houston
Finding protein in your dog or cat's urine can be worrying, especially if kidney blood tests still look fairly normal. The kidneys can lose their ability to retain protein before their overall filtering function is severely reduced.
However, a positive urine dipstick is the beginning of an investigation, not a diagnosis of glomerulonephritis. Where the protein comes from and whether the loss persists determine the next step.
Quick Answer
Glomerulonephritis is inflammation affecting the kidney's microscopic filters and is one cause of protein-losing kidney disease. Vets first confirm persistent renal protein loss and exclude causes such as urinary inflammation or infection. Treatment targets the underlying disease, urine protein loss, blood pressure and complications. Severe weakness, breathing difficulty, collapse or sudden neurological signs require urgent care.
Why does protein loss matter?
Glomeruli normally retain most important blood proteins while filtering fluid and small waste molecules. Damage can allow albumin to escape into urine. Substantial losses may contribute to low blood albumin, fluid accumulation and an increased risk of abnormal blood clots.
Glomerular disease may also cause chronic kidney disease or acute kidney injury. It is not a completely separate condition in which kidney failure cannot occur. Merck's glomerular disease review describes both protein-loss complications and reduced kidney function.
Does proteinuria always mean glomerulonephritis?
No. Proteinuria simply means protein is present in urine. Blood, inflammation or infection in the urinary tract can contribute. Temporary changes also occur, and some kidney protein loss arises from disorders other than inflammatory glomerular disease.
Other possibilities include amyloidosis, inherited kidney abnormalities, systemic hypertension and damage associated with infections or inflammatory diseases elsewhere. Cats and dogs differ in how commonly particular glomerular disorders occur.
How is protein loss measured?
A urine protein-to-creatinine ratio, or UPC, helps quantify loss. It should be interpreted with a urine sediment examination and sometimes culture, then repeated when appropriate to establish persistence.
For stable patients, IRIS considers UPC above 0.5 in dogs and above 0.4 in cats proteinuric, once non-renal explanations have been excluded. These thresholds do not diagnose a particular biopsy pattern. IRIS guidance on early kidney assessment explains the need to interpret protein loss with other findings.
Which findings are more concerning?
| Finding | Meaning and action |
|---|---|
| One abnormal dipstick in an otherwise well animal | Arrange proper urine assessment rather than self-treating. |
| Persistent raised UPC or increasing protein loss | Investigate kidney and systemic causes and discuss treatment. |
| Low albumin, swelling, abdominal fluid or high blood pressure | Prompt assessment for significant complications. |
| Sudden breathing difficulty, collapse or severe limb pain | Emergency care; blood clots and other crises must be considered. |
What tests may be recommended?
The work-up often includes kidney blood values, albumin, cholesterol, blood pressure and urine testing. Infectious disease tests depend on location, travel and exposure. Imaging may reveal another disease or help assess kidney structure.
A kidney biopsy can identify the type of damage and guide decisions about immune-suppressing treatment. It is considered when the result is likely to change care and the procedure is acceptably safe. The IRIS diagnostic consensus for suspected canine glomerular disease supports a staged investigation rather than using UPC alone.
How is treatment chosen?
Medicines that reduce pressure within kidney filters may reduce protein loss, but require monitoring of kidney values, potassium, hydration and blood pressure. Nutrition is adjusted to the disease stage, protein loss and body condition; an extremely protein-restricted homemade diet can worsen muscle loss.
Some animals need treatment for infection, hypertension, swelling or clot risk. Immunosuppression is not appropriate for every proteinuric patient and may be harmful if an infection is present. Consensus guidance on immunosuppressive treatment explains the importance of establishing the likely disease process.
When is this an emergency?
Seek immediate care for breathing distress, collapse, seizures, sudden blindness or a suddenly painful, weak limb. These signs can indicate complications such as thromboembolism or severe hypertension. Repeated vomiting, severe lethargy or markedly reduced urine also requires urgent assessment.
What should you do at home?
- Keep a copy of UPC, albumin, kidney values and blood pressure results so trends are visible.
- Give prescribed medicines consistently and report vomiting or reduced eating before continuing an unchanged plan.
- Record weight, appetite, activity and any swelling or abdominal enlargement.
- Attend early monitoring after medication changes, then follow the individual recheck schedule.
- Ask which treatment goal applies to your animal; there is no universal percentage reduction suitable for every case.
Common mistakes
- Calling all urine protein glomerulonephritis.
- Starting steroids without checking for infection and other causes.
- Assuming normal creatinine means the kidneys are unaffected.
- Skipping rechecks because the animal looks well.
- Using human diuretics or supplements for swelling.
Can this be prevented?
Not every cause is preventable. Appropriate parasite control, prompt investigation of infection and regular monitoring of at-risk animals can reduce avoidable problems. Maintain comfortable activity and adequate nutrition rather than forcing exercise in a weak or swollen patient.
Frequently asked questions
Can glomerular disease be present without symptoms?
Yes. Urine testing may identify protein loss before obvious illness.
Does every patient need a biopsy?
No. The likely benefit must outweigh the procedural risk and the result should meaningfully affect decisions.
Can protein loss improve?
It can, depending on the cause and response to treatment. Continued monitoring is needed even after improvement.
What is nephrotic syndrome?
It describes a combination of marked urine protein loss, low albumin, high cholesterol and fluid accumulation, indicating serious disease.
Protein in urine deserves a careful explanation, not an instant worst-case label. Confirm its source, measure its persistence and use the whole patient to guide care.
For help preparing questions about urine results and ongoing kidney monitoring, visit ASK A VET™.
