Proteinuria in Dogs

Proteinuria is the presence of excessive protein in the urine, released from the glomerulus, the filtering unit of the kidney. Normal urine contains only small amounts of protein.

The anatomical structure of the filtering unit of the kidneys restricts the passage of proteins over a certain size. Albumin, an important blood protein, constitutes only a small portion of the protein normally present in urine. Smaller proteins can pass freely through the glomerulus, but are largely reabsorbed by the cells of the kidney tubules.

There are 3 classifications of proteinuria:

Preglomerular

Postglomerular

Glomerular

Glomerular proteinuria is the result of damage to the glomerulus. Large amounts of albumin are lost through the glomerulus.

Causes of Glomerular Proteinuria

There are a number of disorders associated with glomerular proteinuria including:

Immune-mediated disease (systemic lupus erythematosus)

Infectious diseases such as ehrlichiosis, Lyme disease and chronic bacterial infections

Diabetes mellitus

Pituitary-dependent hyperadrenocorticism (Cushing's disease)

Hypertension (high blood pressure)

Hereditary forms

Inflammatory (from circulating antigen-antibody complexes, heartworm disease)

Amyloidosis (the deposition of a body protein, amyloid A, the result of a chronic inflammatory process)

Animals with glomerular proteinuria are described as having glomerulonephritis or a glomerulonephropathy.

Diagnostic Approach

Diagnostic tests needed to identify proteinuria include:

Urinalysis

Urine protein/creatinine ratio to determine the severity of protein loss in the urine

General health screen including blood pressure determination

Clinical Signs

Clinical signs may be subtle until significant protein loss has occurred or may reflect the underlying disease

Most animals present with signs of anorexia (loss of appetite), vomiting, weight loss, depression and weakness

Dogs average age of onset is between 7-8 years

Familial forms have been recognized in : Doberman pinschers, Samoyeds, Rottweilers, greyhounds, beagles, Bernese mountain dogs, English cocker spaniels, bull terriers and soft-coated wheaton terriers

Familial Amyloidosis has been recognized in shar-peis

Treatment Guidelines

There are three basic treatment objectives:

Identification and elimination of causative antigens

Reduction of glomerular inflammation and fibrin deposition

Adjustment of the immune response to a desired level (immunomodulation)

First identify and correct all underlying processes. Treat any underlying infections and/or cancerous processes. Rule out via diagnostic tests any of the infectious causes or immune-mediated diseases.

Immunosuppressive treatment is controversial. The primary indication for use is if the underlying cause is immune-mediated and responsive to steroids.

For the treatment of proteinuria, the rationale is to decrease the magnitude of urinary protein loss by feeding a moderately restricted protein diet.

Low protein, low phosphorus diets should be given to pets in kidney failure. Low salt diets should be given to pets with high blood pressure (hypertension). Diets supplemented with omega-3 fatty acids to limit the inflammatory response.

A very low dose of aspirin may be given to prevent blood clot formation. Medications may be prescribed to control blood pressure in pets that are hypertensive. One type of antihypertensive medication called angiotensin converting enzyme (ACE) inhibitors (e.g. enalapril) have been shown to decrease protein loss through the kidneys.

Home Care

Administer any medications prescribed by your veterinarian.

Observe your pet's overall attitude and appetite and watch for evidence of enlargement of the abdomen (ascites) or swelling (edema) of the paws, limbs or face that could indicate development of fluid accumulation from the low protein

Observe your pet for difficulty breathing or limb weakness that may indicate development of thromboembolism (blood clot). Also watch for increased water consumption and urination, vomiting, lethargy or loss of appetite

Schedule regular follow-up visits with your veterinarian.