The kidneys filter water and small molecules from the bloodstream and into the renal tubules. Water and essential molecules are reabsorbed from the tubules and the remaining waste products and a small amount of water are excreted as urine. The microscopic filters of the kidney are called glomeruli (singular, glomerulus), which are small tufts of capillary blood vessels that act as a sieve, allowing small substances to pass through while keeping larger substances such as proteins and blood cells in the bloodstream.

Glomeruli can be damaged by inflammation and become leaky. This is called glomerulonephritis. Very large things, such as red and white blood cells, still are not filtered but some substances not normally filtered like proteins leak through the inflamed glomeruli into the urine. The excessive loss of protein in the urine is called proteinuria, and this condition can adversely affect your pet's health.

Glomerulonephritis occurs when large numbers of immune complexes – these are antigen-antibody complexes – circulating in the bloodstream become trapped in the glomeruli as they attempt to pass into the urine. Deposition of immune complexes triggers an inflammatory reaction that damages the glomeruli and results in proteinuria. The antigens bound to the antibodies in the immune complexes arise as a result of some chronic infectious, inflammatory or cancerous disease process. Several diseases have the potential to result in glomerulonephritis.

The clinical symptoms of glomerulonephritis are quite variable.

Affected dogs may have no symptoms at all. In this instance, glomerular disease first is suspected by the finding of proteinuria on a routine urinalysis.

Some dogs may have signs of chronic kidney failure such as poor appetite, lethargy, weight loss, poor hair coat, excessive urination and excessive water consumption.

Some dogs may have symptoms related to sudden blockage of major blood vessels by a blood clot (thromboembolism). Vessels commonly blocked include the lung arteries, which causes rapid breathing or panting, rapid heart rate and high body temperature, and iliac arteries, which causes sudden loss of use of the rear limbs. Thromboembolism is a medical emergency and your pet should be seen by a veterinarian promptly.

Some dogs may have symptoms related to systemic hypertension. Often the first symptom recognized is acute onset of blindness due to detachment of the retina or bleeding into the retina. This complication is a medical emergency and your pet should be seen by a veterinarian promptly.

Some dogs may have symptoms of an underlying infectious, inflammatory or cancerous disease process that predisposes the animal to glomerulonephritis.

Some dogs may have symptoms of subcutaneous edema, including swollen paws, face, hocks (ankles) or scrotum in males, or a swollen abdomen caused by fluid accumulation, known as ascites.

Causes

Viral infections

Infectious hepatitis in dogs (canine adenovirus 1)

Bacterial infections

Lyme disease (borreliosis)

Ehrlichiosis (an infectious disease transmitted by ticks)

Rocky Mountain Spotted Fever (another disease transmitted by ticks)

Brucellosis (an infectious disease)

Dermatitis (infection of the skin)

Gingivitis (infection of the gums)

Endocarditis (infection of the heart valves)

Prostatitis (infection of the prostate)

Pyometra (infection of the uterus)

Chronic fungal infections

Heartworm disease

Leishmaniasis (a protozoal infection rarely encountered in the United States and transmitted by sandflies)

Non-infectious inflammatory diseases that have been associated with glomerulonephritis include:

Pancreatitis (inflammation of the pancreas)

Immune-mediated polyarthritis (inflammation of the joints)

Systemic lupus erythematosus (an autoimmune disorder)

Neoplasia (cancer)

Lymphosarcoma

Mast cell tumor

Other tumors

Despite the long list of infectious, inflammatory and neoplastic disease processes that can result in glomerulonephritis, in as many as 75 to 80 percent of dogs and cats with glomerulonephritis, the underlying cause cannot be identified and the disorder is referred to as "idiopathic."

Many other medical problems can lead to symptoms similar to those encountered in pets with glomerulonephritis. It is important to exclude these conditions before establishing a definitive diagnosis.