Glomerulonephritis (a cause of proteinuria)

KidneyDiseasesMeongsiljang Veterinary Advisory Board

Glomerulonephritis is a condition in which inflammation of the kidney’s filtering units causes protein to leak into the urine. The key signs are proteinuria, swelling, and high blood pressure. Early detection and ongoing management are essential to slow the progression to kidney failure.

What is glomerulonephritis? A kidney disease causing proteinuria

An illustration of a kidney cross-section explaining the concept of glomerulonephritis

Glomerulonephritis is a kidney disease in which inflammation of the glomeruli—the tiny filters that cleanse the blood—causes protein to leak into the urine. Early detection is crucial. Even if your pet appears perfectly healthy, the presence of protein in the urine signals that these filters are already being damaged. If proteinuria is detected on a urinalysis, do not wait more than two weeks; seek a comprehensive diagnostic workup immediately.

Why does it occur? Main causes and pathogenesis

Glomerulonephritis typically begins when pre-formed immune complexes deposit on the glomerular basement membrane, or when circulating antibodies bind to antigens and trigger inflammation. This immune response activates the complement system, promotes platelet aggregation, and stimulates the coagulation cascade, ultimately allowing protein to leak through the glomeruli. Underlying diseases often act as the trigger.

Chronic infections: Prolonged infections such as heartworm disease, Lyme disease, feline leukemia virus (FeLV), and periodontal disease can cause the immune response to attack the glomeruli.

Autoimmune diseases: Conditions like systemic lupus erythematosus, in which the body attacks its own tissues.

Chronic inflammation: Long-standing inflammatory states such as pancreatitis and enteritis.

Idiopathic: In many cases, the cause remains elusive. One study of 106 dogs with glomerular disease found that the underlying cause could not be identified in approximately 43% of cases.

Key symptom checklist — Don’t miss these signs

Glomerulonephritis is often called a "silent progressive disease" because it shows few symptoms in its early stages. If you notice any of the following signs, your pet should undergo urine and blood tests.

Foamy urine: Bubbles persist in the urine and do not disappear quickly.

Edema: Swelling occurs in the legs, abdomen, or face, accompanied by sudden weight gain.

Decreased appetite: Food intake noticeably drops compared to usual.

Weight loss: Muscle wasting leads to a visibly thin appearance.

Lethargy: Reduced activity levels and increased sleep.

High blood pressure: May manifest as abnormal pupil response or sudden vision loss.

A pet owner checking for foam in the urine and swelling.

Emergency signs requiring immediate veterinary care

If you notice any of the following symptoms, it indicates that glomerulonephritis has acutely worsened or complications have begun. Emergency veterinary care is required within 24 hours. - Labored breathing and frequent coughing (suspected pulmonary edema) - Sudden blindness or unequal pupils (hypertensive retinal detachment) - Blood in the urine or a sudden decrease in urine output - Vomiting and complete loss of appetite lasting more than 24 hours - One leg suddenly becoming cold and showing signs of paralysis (thromboembolism)

How is it diagnosed?

Diagnosing glomerulonephritis centers on identifying the cause of proteinuria. Since a routine urinalysis alone cannot determine the precise condition, a stepwise diagnostic approach is necessary. Urine Protein-to-Creatinine Ratio (UPC): A value of 0.5 or higher in dogs, or 0.4 or higher in cats, indicates significant proteinuria. Blood tests: To assess albumin, cholesterol, and kidney function markers (BUN, creatinine, and SDMA). Blood pressure measurement: To check for the presence of hypertension. Infection screening: To rule out heartworm disease and tick-borne illnesses. Renal ultrasound: To evaluate structural changes and differentiate from other diseases.

Stages based on urine protein-to-creatinine ratio (UPC)

Item	Normal	Borderline	Overt Proteinuria
Dog UPC	< 0.2	0.2 – 0.5	> 0.5
Cat UPC	< 0.2	0.2 – 0.4	> 0.4
Recommended Action	Regular check-ups	Recheck within 2–4 weeks	Immediate detailed examination

Based on IRIS (International Renal Interest Society) guidelines

How is treatment managed?

Treatment for glomerulonephritis follows three main pillars: removing the underlying cause, reducing proteinuria, and managing complications. The goal is not necessarily a cure, but rather slowing disease progression and maintaining your pet’s quality of life.

Treating the underlying cause: If an infection is present, antibiotics or antiparasitic treatments are used; if an autoimmune condition is involved, immunosuppressive medications may be considered.

ACE inhibitors/ARBs: These medications lower pressure within the glomeruli to reduce protein leakage.

Low-protein, low-sodium renal prescription diet: Helps decrease the workload on the glomeruli.

Omega-3 supplementation: Shown to have anti-inflammatory effects.

Antithrombotic agents: Prescribed to prevent blood clots if albumin levels drop significantly.

Your veterinarian will determine the appropriate dosage and medications based on your pet’s weight and test results.

A veterinarian preparing renal prescription diets and medications

Essential home care points

Daily care is just as important as medication. The following points determine the progression rate of proteinuria.

Strict adherence to renal prescription diet: No treats or human food; controlling protein and sodium is key.

Hydration: Always provide fresh water; for cats, use wet food and water fountains.

Regular monitoring: Check UPC, blood pressure, and blood work every 2–3 months.

Weight tracking: Weigh your pet once a week—sudden weight gain may signal edema.

Minimize stress: Avoid factors that raise blood pressure.

Oral care: Periodontal disease is a common cause of immune complex formation.

Checking your pet's weight and water intake at home

Breed-specific precautions and tips to prevent recurrence

Certain breeds are genetically predisposed to a higher risk of glomerular disease, making earlier screening essential. · Samoyeds, Dobermans, and Bull Terriers: Reported family history of hereditary glomerular disease (hereditary nephropathy) · Soft Coated Wheaten Terriers: Increased risk of concurrent protein-losing nephropathy and enteropathy · Abyssinians and certain other cat breeds: Predisposition to renal amyloidosis (confirmed via positive Congo red staining) · Annual urine and blood pressure testing is recommended for pets aged 7–8 years and older, who fall into the high-risk age group. · Never discontinue treatment without consulting your veterinarian.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently asked questions

Is glomerulonephritis curable?

If the underlying cause is an infection or a treatable condition, improvement is possible. However, in most cases, it’s managed as a chronic condition focused on slowing disease progression and controlling proteinuria. The earlier it’s detected, the better the management outcomes tend to be.

Does foamy urine always mean glomerulonephritis?

Not necessarily. Normal urine can sometimes temporarily develop foam. However, if the foam persists for several minutes and keeps recurring, it’s important to have a UPC test done. It’s the quickest and most accurate way to check.

Is it really necessary to feed a kidney prescription diet?

Yes, once proteinuria is confirmed, prescription diet is just as important as medication. Regular pet food tends to be high in protein, phosphorus, and sodium, which can increase the burden on the glomeruli. Please consult with your veterinarian to choose the most suitable product for your pet.

Can supplements or omega-3s help?

Studies suggest that omega-3 fatty acids (EPA and DHA) can help alleviate glomerular inflammation, which is why they are often used as a complementary therapy. However, because they may interact with other medications, it is essential to consult your veterinarian before starting this treatment.

My pet shows no symptoms, but a recent check-up revealed protein in the urine. Does this require immediate treatment?

If the results fall within the borderline range, we recommend retesting in 2–4 weeks to confirm whether the condition persists. If persistent proteinuria is confirmed, further diagnostic testing will be conducted to identify the underlying cause. Please remember that the absence of symptoms does not necessarily mean everything is fine.

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References

[1] Ettinger SJ, Feldman EC, Cote E. Textbook of Veterinary Internal Medicine, 8th Edition. Elsevier, 2017 — Glomerular Disease Chapter

[2] Nelson RW, Couto CG. Small Animal Internal Medicine, 6th Edition. Elsevier, 2019 — Glomerulonephritis and Proteinuria

[3] IRIS (International Renal Interest Society) Consensus Guidelines on Glomerular Disease, 2013