CONDITION
Glomerulonephritis
Glomerulonephritis describes inflammation of the glomeruli — the tiny filtering units inside the kidneys that clean the blood and produce urine. When these filters become inflamed, they may leak protein into the urine or allow waste products to build up in the bloodstream, and in some cases both processes occur together. The condition can develop suddenly or progress quietly over months, and the underlying cause is not always apparent at the time it is recognised. Owners often arrive at this page after routine bloodwork or urine testing has shown changes such as protein in the urine, elevated kidney values, or low albumin in the blood. Some dogs or cats show visible signs such as reduced appetite, weight loss, or swelling in the legs or abdomen, while others appear well and the findings emerge during screening for another concern. The pattern of signs depends on how much the filtering function has been affected and whether the condition has triggered secondary changes elsewhere in the body. This page explores what glomerulonephritis may look like in daily life, what processes underneath can lead to inflammation of the kidney filters, how the condition is investigated through blood tests, urine analysis, and sometimes tissue sampling, and the range of approaches that exist to address the inflammation, support kidney function, and manage complications that may develop over time.
Why this matters now
Glomerulonephritis can appear at any age, but middle-aged to older dogs are more commonly affected, particularly certain breeds including Soft Coated Wheaten Terriers, English Cocker Spaniels, and Bernese Mountain Dogs. In cats, the condition tends to be recognised less frequently and may emerge at varying life stages. The inflammation can develop following persistent infections elsewhere in the body, immune-mediated processes, or as part of a wider pattern that includes high blood pressure or blood clotting changes, though in many cases no clear trigger is identified at the outset.
The course can vary considerably between individuals. Some animals show a gradual decline in kidney function over months to years, with protein loss increasing slowly and clinical signs emerging in stages. Others experience a more rapid progression, with noticeable changes in appetite, energy, or fluid balance appearing over weeks. The trajectory often depends on the extent of glomerular damage, whether the underlying cause can be identified and addressed, and how the body responds to early filtering changes.
Signals & patterns
Early signals
Subtle changes in thirst or urination
An owner may notice the water bowl needs refilling more often, or that their dog or cat is asking to go outside more frequently. These shifts can be mild and easy to attribute to weather or routine changes, but they may reflect the kidneys' altered handling of fluid as the glomeruli begin to leak protein or lose filtering efficiency.
Reduced appetite or selective eating
Some animals become less interested in their usual food or begin to pick at meals rather than finishing them. This can occur as waste products start to accumulate in the bloodstream, creating a mild sense of nausea or discomfort that the animal cannot articulate but expresses through eating behaviour.
Weight loss despite normal activity
Gradual weight loss may be noticed over weeks to months, even when the animal remains reasonably active and engaged. The loss often reflects a combination of reduced food intake and ongoing protein loss through the urine, which the body cannot fully compensate for through diet alone.
Foamy or unusually concentrated urine
When significant amounts of protein are passing into the urine, it may appear foamy in the litter tray or on grass, similar to beaten egg white. This visible change is not present in all cases, but when it occurs it can be one of the first tangible signs that the kidney filters are allowing larger molecules through.
Later signals
Swelling in the legs, face, or abdomen
Fluid may begin to accumulate under the skin or inside the abdomen when albumin levels in the blood drop low enough to disturb the normal balance of fluid between blood vessels and surrounding tissues. The swelling often appears soft and pits when pressed, and may be most visible in areas with less fur or looser skin.
Marked lethargy or withdrawal
As kidney function declines further and waste products build up, many animals become noticeably less active, spending more time resting and showing less interest in play, walks, or interaction. This shift reflects the accumulation of uraemic toxins and the metabolic burden placed on other organ systems.
Sudden breathlessness or laboured breathing
In some cases, fluid can accumulate in the chest or lungs, either because of very low albumin levels or because a blood clot has formed in the pulmonary circulation. Breathing may become rapid, shallow, or effortful, and the animal may adopt a hunched posture or extend the neck to ease airflow.
Click to read about the biological mechanisms
How this is usually investigated
Investigation typically begins with a review of the animal's history—including any recent infections, medications, or changes in thirst and urination—and a physical examination to assess hydration, body condition, and signs of fluid accumulation. Blood and urine tests form the foundation of the diagnostic picture, revealing the extent of protein loss, kidney function, and any secondary metabolic changes. In some cases, imaging or tissue sampling may be pursued to clarify the type and severity of glomerular damage or to search for underlying causes that may not be apparent from initial screening.
Urine protein-to-creatinine ratio
Blood biochemistry and haematology
Blood pressure measurement
Abdominal ultrasound
Renal biopsy and histopathology
Options & trade-offs
Management is usually assembled from several components, tailored to the individual animal's degree of protein loss, kidney function, blood pressure, and tolerance of dietary change or medication. Different combinations suit different households, and the approach may shift over time as the condition evolves or as the owner observes what the animal accepts most readily. No single strategy addresses all aspects of the condition, and many animals receive overlapping interventions aimed at slowing progression, reducing protein loss, and managing complications.
Dietary modification
Feeding a diet with controlled protein quantity and quality, reduced phosphorus, and sometimes added omega-3 fatty acids can lessen the metabolic burden on damaged glomeruli and may help to reduce proteinuria and slow progression of kidney damage. Some formulations are designed specifically for kidney support, while others are general low-protein diets adapted to the individual's palatability preferences and body condition. The change is often introduced gradually to allow the animal to adjust to the new taste and texture.
Trade-offs: Not all animals accept unfamiliar foods readily, and prolonged refusal can lead to weight loss or nutritional deficiencies. The degree of protein restriction that is both safe and beneficial varies between individuals, and excessively low protein intake may contribute to muscle wasting if not carefully monitored.
ACE inhibitors or angiotensin receptor blockers
These medications reduce pressure within the glomerular capillaries by dilating the blood vessels that carry blood away from the filtering units, which can decrease the leakage of protein into the urine and may slow the rate of glomerular scarring. They are typically given once or twice daily by mouth, and the dose may be adjusted based on blood pressure readings and changes in kidney values over time.
Trade-offs: A small proportion of animals experience a temporary rise in creatinine when therapy is started, reflecting reduced filtering pressure, and this may require dose adjustment or temporary discontinuation. The medications do not reverse existing glomerular damage, and their effect on protein loss varies between individuals.
Immunosuppressive therapy
Drugs such as corticosteroids, cyclophosphamide, or mycophenolate may be considered when biopsy findings or clinical patterns suggest an immune-mediated component, with the aim of reducing the inflammatory attack on the glomeruli. Treatment is usually introduced at a higher dose and then tapered over weeks to months, with regular blood monitoring to watch for side effects such as increased infection risk, gastrointestinal upset, or changes in liver or bone marrow function.
Trade-offs: The response to immunosuppression is unpredictable, and some animals show little change in protein loss or kidney function despite several weeks of therapy. The medications carry risks of secondary infections, behavioural changes, or organ toxicity, and the decision to use them often depends on the severity of protein loss and the histological pattern seen on biopsy.
Anticoagulant or antiplatelet therapy
In animals that have developed a hypercoagulable state—indicated by low antithrombin levels or evidence of clot formation—low-dose aspirin or other antiplatelet agents may be given to reduce the risk of thromboembolic events such as pulmonary clots or limb ischaemia. The dose is typically lower than that used for pain relief, and the aim is to gently inhibit platelet aggregation without causing excessive bleeding.
Trade-offs: Monitoring is less straightforward than with some other interventions, as routine clotting tests do not always reflect platelet function or clot risk accurately. The benefit in preventing clinically significant clots is difficult to quantify in individual animals, and prolonged use carries a small risk of gastrointestinal irritation or bleeding.
Blood pressure management
When systemic hypertension is present, medications such as amlodipine may be introduced to lower blood pressure and reduce the risk of damage to the eyes, brain, and heart, as well as to lessen the strain on the remaining functional glomeruli. Blood pressure is typically rechecked at intervals after starting treatment to guide dose adjustments.
Trade-offs: Lowering blood pressure too rapidly or too far can reduce perfusion to the kidneys and other organs, potentially worsening kidney function transiently. Home blood pressure monitoring is not always practical, so adjustments are usually made based on clinic readings, which may not fully reflect the animal's resting state.
Common misconceptions
"Glomerulonephritis is always caused by an infection that can be cleared with antibiotics."
While some cases develop after or alongside infections elsewhere in the body, the glomerular inflammation is often driven by immune complexes or antibodies that persist even after the original infection has resolved. In many animals, no active infection is found at the time of diagnosis, and antibiotics alone do not reverse the glomerular damage.
"Once protein appears in the urine, kidney failure is inevitable and nothing can slow it down."
The trajectory varies widely between individuals, and some animals remain stable for months to years with supportive management, particularly when protein loss is modest and kidney function is still well preserved. Interventions such as dietary change, blood pressure control, and ACE inhibitors can reduce the rate of progression in many cases, though the degree of response differs.
"A low-protein diet will starve the animal or cause them to lose muscle rapidly."
When protein quantity and quality are carefully balanced and the diet provides adequate calories, most animals maintain body condition and muscle mass without difficulty. Excessive protein restriction can indeed contribute to muscle wasting, but the formulations used in kidney support are designed to meet nutritional needs while reducing the metabolic load on damaged glomeruli, and adjustments can be made if body condition declines.
Related conditions
Nephrotic Syndrome
Nephrotic syndrome describes the pattern that can emerge when glomerulonephritis causes severe protein loss through damaged kidney filters, leading to low albumin in the blood and often swelling in the limbs or abdomen. The two terms describe overlapping aspects of the same underlying process—glomerulonephritis refers to the inflammation itself, while nephrotic syndrome refers to the collection of changes that may follow when that inflammation becomes pronounced.
Acute Kidney Injury
Glomerulonephritis can occasionally present as acute kidney injury when the inflammation develops rapidly or becomes severe enough to interfere with filtration over a short period. In other cases, acute kidney injury from another cause may be considered during the early stages of investigation, before urine protein patterns and other findings point more clearly toward glomerular inflammation.
Protein-Losing Enteropathy
Protein-losing enteropathy shares the pattern of low albumin in the blood, but the protein is lost through the intestinal wall rather than the kidneys. Distinguishing between the two often involves careful urine testing, as glomerulonephritis typically produces marked protein in the urine while protein-losing enteropathy does not.
Lyme Nephritis
Lyme nephritis is a specific form of glomerulonephritis triggered by the immune response to Borrelia burgdorferi infection in dogs. It represents one of the infectious causes that can lead to glomerular inflammation, and tends to appear in younger dogs in areas where the tick-borne bacterium is present.
Systemic Hypertension in Cats
Systemic hypertension can develop as a consequence of glomerulonephritis when kidney function is affected, and in turn high blood pressure may worsen the damage to the glomeruli over time. Monitoring and managing blood pressure often becomes part of the broader approach to supporting kidney health in dogs and cats with glomerular disease.
Understanding how the kidneys interact with fluid balance, blood pressure, and protein metabolism can provide useful context for interpreting changes over time and for conversations about monitoring intervals or adjustments to management. The metabolic health pillar includes related patterns such as chronic kidney disease and protein-losing conditions, which may overlap with glomerulonephritis in some animals. Observations about appetite, thirst, weight, and energy level at home often inform decisions about when to recheck blood or urine values, and keeping a loose record of these patterns can be a helpful reference when reviewing progress.