Glomerular Nephritis

Glomerular nephritis, more precisely termed glomerulonephritis, is an inflammatory condition affecting the glomeruli, the microscopic filtering units within the kidneys. Each canine kidney contains hundreds of thousands of glomeruli, each consisting of a tuft of specialized capillaries surrounded by a structure called Bowman's capsule. These glomeruli perform the critical function of filtering blood to remove waste products while retaining essential proteins and blood cells. When the glomeruli become inflamed and damaged, this filtering function breaks down, allowing large proteins, particularly albumin, to leak into the urine.

The glomerular filtration barrier is an exquisitely designed three-layer structure composed of the fenestrated capillary endothelium, the glomerular basement membrane, and the podocyte foot processes with their interposed slit diaphragms. This barrier is selectively permeable, allowing water, electrolytes, and small waste molecules to pass through while preventing the passage of larger molecules such as albumin (approximately 69 kilodaltons). Damage to any component of this barrier disrupts its selectivity and leads to proteinuria, the hallmark of glomerular disease.

Glomerulonephritis in dogs is predominantly an immune-mediated process. The most common mechanism involves the deposition of immune complexes, circulating antibody-antigen complexes, within the glomerular structures. These immune complexes become trapped in the glomerular capillary walls or mesangium (the supportive tissue between capillary loops) and trigger a local inflammatory response that damages the filtration barrier. The antigens involved may originate from chronic infections, neoplasia, autoimmune diseases, or in many cases, remain unidentified.

The consequences of sustained glomerular damage extend far beyond simple protein loss. As proteinuria becomes severe and persistent, the dog develops hypoalbuminemia (low blood albumin), which reduces plasma oncotic pressure and leads to fluid shifts, resulting in edema and body cavity effusions. The urinary loss of antithrombin III, an important anticoagulation protein, predisposes affected dogs to thromboembolic events, which represent one of the most dangerous complications of glomerular disease. Progressive glomerular inflammation and scarring (glomerulosclerosis) ultimately lead to loss of functional nephrons and chronic kidney disease.

Glomerulonephritis can occur at any age but is most commonly diagnosed in middle-aged to older dogs, with a reported mean age of onset between 6 and 7 years. The condition may remain subclinical for extended periods, with proteinuria detectable on routine urinalysis long before the dog shows outward signs of illness. This makes routine health screening, including urinalysis with urine protein-to-creatinine ratio measurement, particularly important in breeds known to be predisposed to glomerular disease.

The causes of glomerulonephritis in dogs are diverse, and in many cases the specific triggering antigen is never identified despite thorough diagnostic investigation. The unifying pathogenic mechanism is immune complex formation and deposition, but the source of the antigens driving this process varies widely. Understanding the potential underlying conditions is essential because successful management of glomerulonephritis often requires identification and treatment of the primary disease.

Chronic infectious diseases are among the most well-documented causes of glomerulonephritis in dogs. Ehrlichiosis, caused by the tick-borne rickettsial organism Ehrlichia canis, is strongly associated with immune complex glomerulonephritis, particularly in endemic regions. Borreliosis (Lyme disease) caused by Borrelia burgdorferi is another tick-borne infection with a well-established connection to glomerular disease, and a specific form called Lyme nephritis can cause rapidly progressive and often fatal glomerulonephritis, particularly in Labrador Retrievers and Golden Retrievers.

Other infectious causes include leishmaniasis, which is a major cause of glomerulonephritis in endemic areas of Europe, South America, and parts of Asia. Heartworm disease (dirofilariasis) produces circulating antigens that can form immune complexes and deposit in the glomeruli. Chronic bacterial infections, including pyometra, endocarditis, discospondylitis, and chronic pyoderma, generate sustained antigenemia that drives immune complex formation. Chronic viral infections, though less commonly documented in dogs than in humans, may also contribute.

Neoplasia is another important underlying cause of glomerulonephritis. Tumor-associated antigens enter the circulation and form immune complexes that deposit in the glomeruli. The types of neoplasia most commonly associated with glomerulonephritis include lymphoma, mastocytosis, and various carcinomas. In some cases, glomerulonephritis is identified before the underlying tumor is diagnosed, and the presence of unexplained proteinuria in a middle-aged or older dog should prompt consideration of occult neoplasia.

Autoimmune and inflammatory conditions, including systemic lupus erythematosus (SLE), polyarthritis, and inflammatory bowel disease, are recognized causes of glomerulonephritis in dogs. In SLE, anti-nuclear antibodies form immune complexes that deposit in multiple tissues including the glomeruli, skin, and joints. Hereditary forms of glomerular disease occur in several breeds, including the Soft Coated Wheaten Terrier, which develops a breed-specific protein-losing nephropathy and enteropathy, and the English Cocker Spaniel, which is prone to a familial nephropathy that progresses to end-stage renal failure. Despite thorough investigation, approximately 50 to 75 percent of canine glomerulonephritis cases are classified as idiopathic, meaning no underlying cause can be identified.

The clinical presentation of glomerulonephritis in dogs is often insidious, with the earliest stages producing no visible symptoms at all. Proteinuria may be the only abnormality detectable for months or even years before clinical signs develop, which is why routine urinalysis is such a valuable screening tool. When symptoms do appear, they often reflect the systemic consequences of sustained protein loss rather than the renal disease itself, which can make the condition challenging to recognize without laboratory testing.

The most common early clinical sign noticed by owners is weight loss despite a normal or even increased appetite. As albumin is progressively lost through the kidneys, the body attempts to compensate by increasing hepatic albumin synthesis, which draws on protein reserves and energy stores. Muscle wasting may become apparent, particularly along the topline and over the hindquarters. The dog may appear generally thinner despite adequate food intake, prompting owners to seek veterinary attention.

As hypoalbuminemia becomes more pronounced, fluid accumulation in body tissues and cavities becomes clinically evident. Subcutaneous edema, particularly of the limbs and ventral abdomen, may develop. Ascites (abdominal effusion) is one of the more dramatic presentations, causing visible abdominal distension that may be mistaken for weight gain, pregnancy, or other abdominal conditions. Pleural effusion (fluid around the lungs) can cause respiratory difficulty, manifesting as increased respiratory rate, labored breathing, or exercise intolerance. These signs reflect the loss of plasma oncotic pressure that normally keeps fluid within the vascular space.

Thromboembolic complications represent some of the most acute and dramatic presentations of glomerulonephritis. The loss of antithrombin III and other anticoagulant proteins through the damaged glomeruli creates a hypercoagulable state. Pulmonary thromboembolism (PTE) is the most common and most dangerous thromboembolic event, presenting with sudden onset of severe respiratory distress, cyanosis, collapse, and potentially death. Thrombosis of other vessels, including the aortic trifurcation (saddle thrombus), renal veins, and portal vein, can also occur.

As glomerular disease progresses to chronic kidney disease, additional symptoms emerge that reflect declining renal function. These include increased thirst and urination (polyuria and polydipsia), decreased appetite, nausea and vomiting, lethargy, and dehydration. Systemic hypertension, which frequently accompanies glomerular disease, may cause additional signs including sudden blindness from retinal detachment or hemorrhage, disorientation, and seizures. By the time these advanced signs develop, significant and irreversible kidney damage has typically occurred.

Diagnosis of glomerulonephritis involves a systematic approach beginning with detection of proteinuria and progressing through characterization of the protein loss, assessment of renal function, identification of potential underlying causes, and ultimately, renal biopsy for definitive histopathologic classification. A thorough diagnostic workup is essential because the specific type and severity of glomerular disease directly influence treatment decisions and prognosis.

The diagnostic process typically begins when proteinuria is identified on a routine urinalysis. A positive dipstick protein reaction prompts further quantification using the urine protein-to-creatinine ratio (UPC). A UPC value above 0.5 is considered abnormal in dogs, while values above 2.0 are strongly suggestive of glomerular origin proteinuria. Before attributing proteinuria to glomerular disease, pre-renal and post-renal causes must be excluded. Urinary tract infection, which can cause significant proteinuria, should be ruled out by urine culture. A urine sediment examination that reveals an active sediment (pyuria, bacteriuria, hematuria) suggests lower urinary tract disease rather than or in addition to glomerular pathology.

Serum biochemistry provides critical information about the severity and consequences of the disease. Serum albumin and total protein levels quantify the degree of protein depletion. Blood urea nitrogen (BUN) and creatinine levels, along with symmetric dimethylarginine (SDMA), assess the degree of renal functional impairment. Hypercholesterolemia is commonly observed in dogs with nephrotic syndrome, as the liver upregulates lipid production in response to hypoalbuminemia. Electrolyte abnormalities, particularly hyperphosphatemia and hypocalcemia, may develop as renal function declines.

A comprehensive search for underlying causes is an essential component of the diagnostic workup. This typically includes a complete blood count to look for evidence of chronic infection or inflammation, infectious disease testing (particularly for tick-borne diseases, heartworm, and region-specific infections), antinuclear antibody testing to screen for SLE, thoracic and abdominal imaging to identify occult neoplasia or chronic infections, and blood pressure measurement to document and quantify systemic hypertension.

Renal biopsy is considered the gold standard for definitive diagnosis and classification of glomerular disease. The biopsy specimen is evaluated using light microscopy, immunofluorescence or immunohistochemistry, and transmission electron microscopy. Light microscopy reveals the pattern of glomerular injury (membranous, membranoproliferative, proliferative, or sclerosing). Immunofluorescence identifies the types and distribution of immunoglobulin and complement deposits within the glomeruli. Electron microscopy provides ultrastructural detail about the location and character of immune complex deposits and the status of the podocyte foot processes and basement membrane. The International Renal Interest Society (IRIS) and the World Small Animal Veterinary Association (WSAVA) have developed standardized classification schemes for canine glomerular disease based on biopsy findings.

Medical treatment of glomerulonephritis is multimodal and addresses several simultaneous therapeutic goals: reducing proteinuria, managing the underlying cause if identified, controlling secondary complications, and slowing the progression of chronic kidney disease. Treatment protocols have been refined in recent years based on improved understanding of glomerular pathophysiology and the results of consensus statements from veterinary nephrology groups.

Antiproteinuric therapy is the foundation of treatment. Angiotensin-converting enzyme (ACE) inhibitors, most commonly enalapril or benazepril, are the first-line agents for reducing glomerular proteinuria. These drugs dilate the efferent arteriolar tone of the glomerulus, reducing intraglomerular capillary pressure and thereby decreasing the driving force for protein filtration across the damaged barrier. The dose is titrated based on serial UPC measurements, with the goal of reducing the UPC to below 0.5 if possible, or achieving at least a 50 percent reduction from baseline. Angiotensin receptor blockers (ARBs) such as telmisartan may be used as an alternative or in combination with ACE inhibitors for additional antiproteinuric effect.

Immunosuppressive therapy is indicated when renal biopsy confirms an immune-mediated glomerulonephritis, particularly membranoproliferative or proliferative forms. Mycophenolate mofetil has become a favored immunosuppressive agent for canine glomerulonephritis due to its relatively targeted effect on lymphocyte proliferation and its acceptable side effect profile. Cyclosporine and azathioprine are alternatives. Corticosteroids, while potent immunosuppressants, are used cautiously in glomerular disease because they can exacerbate proteinuria, promote hypercoagulability, and worsen hypertension.

Antithrombotic therapy is critically important because of the high risk of thromboembolic complications associated with glomerular disease. Low-dose aspirin (0.5 to 1 mg/kg once daily) is commonly prescribed for its antiplatelet effect. Clopidogrel may be added or substituted for additional antiplatelet activity. In dogs with severe hypoalbuminemia (below 2.0 g/dL) or documented low antithrombin levels, more aggressive anticoagulation with heparin or low-molecular-weight heparin may be warranted, particularly during periods of acute disease exacerbation or hospitalization.

Dietary modification plays a supportive role in managing glomerulonephritis. A moderate protein restriction diet helps reduce the protein load presented to the damaged glomeruli without causing malnutrition. Diets formulated for renal disease in dogs typically provide high-quality protein in controlled amounts along with restricted phosphorus content and supplemental omega-3 fatty acids. The omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have anti-inflammatory properties that may help modulate glomerular inflammation when supplemented at therapeutic doses.

Antihypertensive therapy is necessary in many dogs with glomerulonephritis, as systemic hypertension is both a consequence and a driver of progressive renal damage. Amlodipine, a calcium channel blocker, is the most commonly used antihypertensive agent in dogs and can be combined with ACE inhibitors for enhanced blood pressure and antiproteinuric effect. Target systolic blood pressure is generally below 160 mmHg, with lower targets preferred if tolerated without adverse effects.

The complications of glomerulonephritis can be life-threatening and require vigilant monitoring and proactive management. Thromboembolic disease, nephrotic syndrome, systemic hypertension, and progressive chronic kidney disease each demand specific therapeutic interventions and ongoing surveillance to prevent catastrophic outcomes.

Thromboembolism is the most immediately dangerous complication and can present with devastating suddenness. Pulmonary thromboembolism manifests as acute respiratory distress with rapid, labored breathing, cyanotic mucous membranes, profound weakness, and collapse. The diagnosis is often suspected clinically and supported by findings on thoracic radiographs (regional hyperlucency, pleural effusion), echocardiography (right heart strain), and arterial blood gas analysis (hypoxemia with a widened alveolar-arterial oxygen gradient). Advanced imaging with computed tomographic angiography (CTA) provides definitive diagnosis but may not be available in all facilities. Treatment involves oxygen supplementation, thrombolytic or anticoagulant therapy, and intensive supportive care, but the prognosis for severe PTE remains guarded.

Nephrotic syndrome, defined as the combination of proteinuria, hypoalbuminemia, hypercholesterolemia, and edema or cavity effusions, represents the full clinical expression of severe glomerular protein loss. Management of the edema and effusions is primarily directed at addressing the underlying hypoalbuminemia through antiproteinuric therapy and, in severe cases, intravenous colloid support with synthetic colloids or plasma transfusions. Diuretics such as furosemide may provide temporary relief of fluid accumulation but must be used cautiously to avoid exacerbating dehydration and renal hypoperfusion.

Systemic hypertension associated with glomerulonephritis requires ongoing monitoring through serial blood pressure measurements. Uncontrolled hypertension accelerates glomerular damage by increasing intraglomerular pressure and further injuring the already compromised filtration barrier. Additionally, severe hypertension can cause target organ damage, most dramatically to the eyes (hypertensive retinopathy with hemorrhage, edema, or detachment), brain (hypertensive encephalopathy presenting as disorientation, seizures, or altered mentation), and heart (left ventricular hypertrophy and eventual cardiac dysfunction).

Progressive chronic kidney disease is the eventual outcome for many dogs with glomerulonephritis, and its management follows the staging and treatment guidelines established by the International Renal Interest Society (IRIS). As kidney function declines, management expands to include phosphate binders to control hyperphosphatemia, anti-nausea medications to manage uremic gastritis, subcutaneous fluid therapy to maintain hydration, erythropoiesis-stimulating agents if anemia develops, and potassium supplementation if hypokalemia occurs. The transition from early glomerular disease management to comprehensive chronic kidney disease management is often gradual and requires regular reassessment of the therapeutic plan.

Quality of life monitoring becomes increasingly important as the disease progresses. Owners should maintain a daily log of appetite, water intake, activity level, and any episodes of vomiting, diarrhea, or behavioral changes. This information helps the veterinary team identify trends and make timely adjustments to the treatment protocol. Regular bloodwork and urinalysis, typically every two to four months in stable patients and more frequently during treatment adjustments, provide objective data to guide therapeutic decisions.

Several breeds have documented genetic predispositions to glomerular disease, and awareness of breed-specific risks enables targeted screening and early intervention. The Soft Coated Wheaten Terrier is perhaps the best-characterized breed in terms of hereditary glomerular disease, carrying a breed-specific condition known as protein-losing nephropathy and enteropathy (PLN/PLE). Affected Wheatens develop glomerulonephritis with concurrent intestinal protein loss, typically presenting in middle age with weight loss, edema, and thromboembolic complications. A genetic test identifying risk-associated variants in the NPHS1 and KIRREL2 genes is commercially available for breeding stock screening.

The Bernese Mountain Dog is predisposed to a form of membranoproliferative glomerulonephritis that tends to present at a relatively young age compared to other breeds. The disease in Bernese Mountain Dogs is often aggressive, progressing to end-stage renal failure within months to a few years of diagnosis. The familial nature of the condition in this breed strongly supports a genetic basis, and breeding programs that screen for proteinuria are recommended to reduce the prevalence of the disease.

The English Cocker Spaniel develops a hereditary nephropathy characterized by glomerular and tubular dysfunction that typically presents in young adulthood. The condition is progressive and ultimately fatal, with affected dogs developing chronic kidney failure by middle age. The Bull Terrier also carries a hereditary nephropathy, specifically a form associated with thickening of the glomerular and tubular basement membranes, sometimes described as a hereditary nephritis similar to Alport syndrome in humans.

The Doberman Pinscher has a documented predisposition to glomerulonephritis that may be related to the breed's susceptibility to chronic hepatitis, von Willebrand disease, and other immune-mediated conditions that can generate circulating immune complexes. Samoyeds carry a hereditary nephritis linked to a defect in the type IV collagen gene, analogous to X-linked Alport syndrome in humans, which affects the structural integrity of the glomerular basement membrane. The condition in Samoyeds is X-linked, so males are more severely affected than females.

Other breeds with recognized predispositions include the Rottweiler, Greyhound, Newfoundland, Miniature Schnauzer, and Labrador Retriever. In Labrador and Golden Retrievers, the association between Lyme disease exposure and Lyme nephritis is a particular concern in tick-endemic regions. Breed-specific screening recommendations vary but generally include annual urinalysis with UPC measurement in predisposed breeds, beginning at three to four years of age, with more frequent monitoring if proteinuria is detected.

Dietary management is a cornerstone of the long-term treatment plan for dogs with glomerulonephritis, and nutritional strategies are tailored to the stage and severity of the disease. The primary dietary goals are to reduce the protein load presented to the damaged glomeruli, provide adequate nutrition to prevent malnutrition despite ongoing urinary protein losses, control phosphorus intake to slow the progression of chronic kidney disease, and supply anti-inflammatory nutrients that may modulate glomerular inflammation.

Protein management in glomerulonephritis requires a nuanced approach. Unlike end-stage chronic kidney disease where severe protein restriction is sometimes recommended to reduce uremic toxin production, moderate protein restriction is generally preferred in glomerular disease to balance the competing needs of reducing proteinuria and preventing protein-calorie malnutrition. The protein that is provided should be of high biological value, meaning it contains a complete amino acid profile that the body can use efficiently. Commercial renal diets are formulated with this balance in mind, providing controlled amounts of high-quality protein sources.

Phosphorus restriction is one of the most evidence-based nutritional interventions for slowing the progression of kidney disease. Excess dietary phosphorus drives secondary hyperparathyroidism and contributes to renal fibrosis and mineralization. Renal diets typically provide phosphorus at levels significantly below those found in maintenance diets. If dietary restriction alone is insufficient to normalize serum phosphorus levels, intestinal phosphate binders such as aluminum hydroxide, calcium carbonate, or lanthanum carbonate are added to meals to reduce phosphorus absorption.

Omega-3 fatty acid supplementation with EPA and DHA from marine sources (fish oil) is recommended for its anti-inflammatory and renal-protective properties. These fatty acids compete with pro-inflammatory omega-6 fatty acids for incorporation into cell membranes and enzymatic pathways, shifting the balance of eicosanoid production toward less inflammatory mediators. Clinical studies in dogs with chronic kidney disease have demonstrated benefits of omega-3 supplementation including reduced proteinuria, slower progression of renal disease, and improved survival times. Therapeutic doses are substantially higher than those found in most commercial diets, typically requiring dedicated fish oil supplementation.

Sodium restriction is recommended in dogs with glomerulonephritis, particularly those with concurrent hypertension or edema. Excessive sodium intake can worsen hypertension and fluid retention, both of which contribute to progressive renal damage. Most commercial renal diets are formulated with controlled sodium levels. High-sodium treats and table foods should be avoided. Adequate caloric intake must be maintained throughout the disease course to prevent weight loss and muscle wasting, which can be challenging as appetite often decreases with advancing kidney disease. Calorie-dense formulations, appetite stimulants such as mirtazapine, and in some cases, assisted feeding through esophagostomy tubes may be necessary to maintain nutritional status.

The prognosis for dogs diagnosed with glomerulonephritis varies considerably depending on the underlying cause, the severity of proteinuria at diagnosis, the presence and extent of azotemia, the histopathologic classification on renal biopsy, and the response to treatment. Dogs diagnosed early with isolated proteinuria and no evidence of renal functional impairment generally have the best prognosis, with survival times potentially extending several years with appropriate management.

Several specific prognostic factors have been identified through clinical research. The magnitude of proteinuria at diagnosis, as measured by the UPC ratio, correlates inversely with survival time. Dogs with UPC values above 8 to 10 carry a significantly worse prognosis than those with lower-grade proteinuria. The response to antiproteinuric therapy is also prognostically significant; dogs that achieve a meaningful reduction in UPC (greater than 50 percent or to below 1.0) generally survive longer than those whose proteinuria remains refractory to treatment.

The degree of azotemia at diagnosis is a strong predictor of outcome. Dogs presenting with normal or mildly elevated creatinine (IRIS stages 1 and 2) have significantly longer survival times than those diagnosed at stage 3 or 4. The presence of nephrotic syndrome at diagnosis carries a guarded prognosis due to the associated risks of thromboembolism and the difficulty of managing severe hypoalbuminemia. Thromboembolic events, when they occur, are associated with high mortality rates regardless of other disease parameters.

Histopathologic classification from renal biopsy provides important prognostic information. Membranous glomerulonephritis, characterized by subepithelial immune complex deposits and basement membrane thickening, may carry a relatively better prognosis than membranoproliferative or proliferative forms, which involve more active inflammation and cellular proliferation. Amyloidosis, which can present similarly to glomerulonephritis, carries a poor prognosis as there is no effective treatment for the amyloid deposition itself. The degree of tubulointerstitial fibrosis and glomerulosclerosis on biopsy reflects the chronicity and irreversibility of the disease process.

For dogs with identified and treatable underlying conditions, the prognosis may be significantly better than for those with idiopathic disease. Successfully treating an underlying infection such as ehrlichiosis or removing a tumor producing glomerulonephritis-inducing antigens can lead to resolution or significant improvement of the glomerular disease. Ongoing monitoring with serial urinalysis, UPC measurements, serum biochemistry, and blood pressure checks is essential for all dogs with glomerulonephritis, regardless of initial response to treatment, to detect early signs of disease progression and adjust therapy accordingly.