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
Options & trade-offs
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