Glomerulonephritis in Dogs and Cats

TL;DR. Glomerulonephritis is a serious, immune-mediated kidney disease in dogs and cats where immune complexes damage the kidneys' filtration system, causing severe protein loss in the urine and potentially leading to chronic kidney failure.

The glomeruli are the delicate filtering units of the kidney that become damaged in glomerulonephritis.

What is it?

Glomerulonephritis (often abbreviated as GN) is a specific type of kidney disease that targets the glomeruli—the microscopic filtering units of the kidneys. In a healthy pet, these tiny structures act as a highly selective sieve. They allow waste products and excess water to pass into the urine while keeping essential components, such as proteins and red blood cells, inside the bloodstream.

When a pet develops glomerulonephritis, their own immune system plays a central role in damaging these filters. The disease is classified as immune-mediated because it is caused by the deposition or local formation of "immune complexes" within the walls of the glomerular capillaries. Immune complexes are microscopic clumps formed when the body's antibodies bind to foreign proteins (antigens). When these clumps lodge in the delicate filters of the kidney, they trigger a cascade of inflammation.

As the inflammation progresses, the kidney's filtering membrane becomes abnormally leaky. This allows vital proteins, particularly albumin, to escape from the blood and pass into the urine—a condition known as proteinuria. Over time, this persistent protein loss can lead to systemic complications, including high blood pressure (hypertension), fluid retention, and progressive chronic kidney disease.

According to a leading veterinary internal medicine reference:

"Acquired glomerulonephritis (GN) is more common in dogs than cats and results from the presence of immune complexes within the glomerular capillary walls..."

Causes & risk factors

Glomerulonephritis is rarely a primary disease; instead, it is typically triggered by an underlying condition that stimulates the immune system to produce antibodies over a prolonged period. These antigens can come from chronic infections, inflammatory diseases, or even certain cancers.

There are two primary ways these damaging immune complexes end up in the kidneys:

1. Circulating complexes: The antibody-antigen clumps form elsewhere in the body and travel through the bloodstream, eventually getting trapped in the narrow capillaries of the glomeruli.
2. In situ formation: Antigens first become physically trapped or localized in the glomerular capillary wall, and passing antibodies bind to them directly on-site.

For example, in dogs suffering from heartworm disease, proteins from the parasite can localize directly in the kidney filters:

"Causes of in situ deposition of immune complexes may be either true autoimmune disease when antibodies are directed against the basement membrane of the glomerular capillaries (not yet documented as a spontaneous disease in dogs and cats) or when antigen becomes localized in the glomerular capillary wall. For example, in dogs with heartworm disease, soluble Dirofilaria immitis antigens have been s[hown to localize there]."

Several dog and cat breeds have documented or suspected genetic predispositions to glomerular diseases. In some breeds, the condition is hereditary and linked to specific genetic mutations or metabolic differences.

Signs to watch for

The clinical signs of glomerulonephritis can vary widely depending on how much protein is being lost and whether the disease has progressed to kidney failure.

Cardinal Sign

• Proteinuria: The presence of excess protein in the urine. This is the hallmark of the disease and is detected through laboratory testing.

Common Signs

• Anorexia: Loss of appetite.
• Lethargy: General sluggishness, weakness, or decreased activity levels.
• Polyuria: Increased frequency or volume of urination.
• Polydipsia: Increased thirst and water consumption.
• Vomiting: Often a sign of accumulating toxins in the blood as kidney function declines.
• Weight loss: Gradual loss of muscle mass and body weight.

Occasional Signs

• Subcutaneous edema: Fluid accumulation causing swelling under the skin, particularly in the limbs or under the chest.
• Ascites: Fluid accumulation in the abdomen, causing a pot-bellied appearance.
• Dyspnea: Labored or difficult breathing, which can occur if fluid builds up in the chest or if a blood clot travels to the lungs.
• Dehydration: Despite drinking more water, the kidneys may lose the ability to conserve fluids.
• Poor body condition and poor haircoat: A dry, brittle coat and loss of muscle tone.
• Paraparesis: Weakness or partial paralysis of the hind limbs.
• Oral ulceration: Sores in the mouth, typically seen in advanced stages of kidney failure.
• Blindness: Sudden loss of vision, which is a direct consequence of severe high blood pressure causing retinal detachment.

Lethargy and fluid swelling (edema) in the limbs are common signs of advanced protein loss.

How vets diagnose it

Diagnosing glomerulonephritis requires a systematic approach to rule out other causes of protein loss and to confirm that the kidneys are the source of the problem. Your vet will begin by investigating any persistent protein in the urine:

"A diagnosis of protein-losing nephropathy (PLN) is made by documentation of persistent proteinuria that cannot be explained by inflammation of the lower urinary tract or blood contamination of the urine. Initial dipstick estimates of urine protein should be evaluated in the light of the urine sediment and specific gravity of the urine."

To fully evaluate your pet, your vet will recommend a comprehensive diagnostic panel:

• Urinalysis & Urine Protein-to-Creatinine (UPC) Ratio: A standard urinalysis checks for protein, blood, and signs of infection. If protein is persistently detected without infection, a UPC ratio is performed to precisely measure the severity of the protein loss.
• Urine Culture: This is performed to rule out a bacterial urinary tract infection, which can mimic or complicate glomerular disease.
• Serum Biochemical Profile & Complete Blood Count (CBC): These blood tests evaluate kidney function (by measuring waste products like urea and creatinine), check blood protein levels (such as albumin), measure cholesterol, and screen for anemia or signs of systemic inflammation.
• Blood Pressure Measurement: High blood pressure is incredibly common in pets with glomerular disease. It occurs due to sodium retention, activation of the renin-angiotensin system, and a lack of natural blood-vessel dilators:

"Systemic hypertension may occur in dogs and cats with glomerular disease caused by sodium retention, activation of the RAS, and impaired release of normal renal vasodilator substances..."

• Plasma Fibrinogen and Antithrombin Concentrations: Because pets with glomerulonephritis lose important clot-preventing proteins (like antithrombin) in their urine, they are at a much higher risk of developing dangerous blood clots. These tests help evaluate your pet's clotting status.
• Occult Heartworm Test: To check for underlying heartworm infection as a potential trigger.
• Thoracic and Abdominal Radiographs & Renal Ultrasonography: Imaging helps visualize the size and structure of the kidneys, screen for fluid in the chest or abdomen, and look for hidden infections or tumors.
• Renal Biopsy (The Gold Standard): While other tests point toward glomerular disease, a kidney biopsy is the only way to definitively diagnose glomerulonephritis and distinguish it from other kidney diseases like amyloidosis. As noted in leading texts:

"Tissue samples should be submitted for routine histopathology, electron microscopy, and immunopathology. Goals of renal biopsy should be to confirm the underlying disease process (specific type of GN, hereditary nephritis, glomerulosclerosis, amyloidosis); determine severity of the disease; and, if possible, determine a prognosis and guide specific therapy."

Renal ultrasound helps veterinarians evaluate the structure of the kidneys and rule out other diseases.

Treatment options

Treatment for glomerulonephritis is multi-faceted. It focuses on reducing protein loss, controlling blood pressure, preventing blood clots, and suppressing the underlying immune response.

First-Line Therapies

• Angiotensin-Converting Enzyme (ACE) Inhibitors (Enalapril or Benazepril): These medications help dilate the blood vessels leaving the kidneys, which lowers the pressure inside the glomeruli and significantly reduces the amount of protein leaking into the urine.
• Platelet Aggregation Reducers (Aspirin): Given at very low doses, aspirin helps prevent the formation of life-threatening blood clots, compensating for the loss of natural anticoagulant proteins in the urine.

Second-Line Therapies

• Calcium Channel Blockers (Amlodipine): If ACE inhibitors alone cannot control your pet's high blood pressure, amlodipine is often added to protect the kidneys, eyes, and brain from hypertensive damage.

Supportive & Immunosuppressive Medications

• Loop Diuretics (Furosemide): Used to help eliminate excess fluid buildup in pets suffering from severe swelling (edema) or abdominal fluid (ascites).
• Aldosterone Antagonists (Spironolactone): Often combined with other diuretics to manage fluid retention and block harmful hormone pathways that damage kidney tissue.
• Immunosuppressants (Azathioprine, Cyclosporine, or Glucocorticoids): These drugs may be prescribed to suppress the abnormal immune response that is creating the damaging immune complexes. However, glucocorticoids must be used with extreme caution, as they can sometimes worsen protein loss in the urine.

Prognosis

Glomerulonephritis has a highly variable course. Some dogs and cats experience spontaneous remission, where the disease resolves on its own or stabilizes with minimal treatment. Others may maintain a relatively stable clinical course, living with ongoing, managed proteinuria for several months to years.

Unfortunately, for some pets, the disease is progressive. Despite aggressive treatment, the ongoing inflammation can lead to irreversible scarring of the kidneys, eventually progressing to chronic renal failure over a period of months to years. Regular monitoring of blood pressure, kidney values, and urine protein levels is essential to adjust therapy and maintain your pet's quality of life.

Prevention

Because primary glomerulonephritis is an immune-mediated condition, there is no direct way to prevent it from developing. However, you can minimize the risk of secondary glomerulonephritis by protecting your pet from known triggers:

• Parasite Prevention: Keep your dog on year-round heartworm prevention to eliminate the risk of heartworm-induced kidney damage.
• Tick Prevention: Use reliable tick preventatives to protect against vector-borne diseases like Lyme disease, which is a known trigger for glomerular inflammation.
• Prompt Medical Care: Treat chronic infections, dental disease, and inflammatory conditions promptly before they can stimulate chronic immune complex production.
• Screening: For breeds predisposed to hereditary kidney diseases, discuss routine urine screening with your veterinarian to catch protein loss in its earliest, most treatable stages.

When to call your vet

Glomerulonephritis can lead to sudden, life-threatening complications. Contact your veterinarian immediately if you notice any of the following red flags:

• Sudden blindness or dilated pupils (a sign of severe high blood pressure).
• Labored, rapid, or difficult breathing (which can indicate a blood clot in the lungs or fluid accumulation in the chest).
• Sudden swelling of the limbs, face, or abdomen.
• Severe vomiting, extreme lethargy, or complete refusal to eat (signs of worsening kidney failure).

For specific breeds

Certain breeds have unique associations with glomerular disease that can help guide your veterinarian's diagnostic and treatment plans:

• Soft Coated Wheaten Terriers: Suspected to have a familial form of membranoproliferative glomerulonephritis that may be associated with an abnormal reaction to dietary proteins.
• Brittany Spaniels: Suspected to have a hereditary deficiency of the third component of complement (C3), a vital part of the immune system, leading to glomerular disease.
• Bernese Mountain Dogs: Often develop glomerulonephritis associated with positive antibody tests for Borrelia burgdorferi (the bacteria that causes Lyme disease).
• Samoyeds: Affected by an X-linked dominant hereditary nephritis.
• English Cocker Spaniels: Affected by an autosomal recessive hereditary nephritis.
• Other Predisposed Breeds: Suspected or documented genetic predispositions also exist in the Siamese Dog, Oriental Shorthair, Chinese Shar-Pei, Beagle, Bull Terrier, Doberman Pinscher, English Foxhound, and Abyssinian Sand Terrier.

Sources

• Textbook of Veterinary Internal Medicine, 5th Edition, pages 692, 696, 1468, 1469.