Proteinuria (Excessive Protein in Urine) in Dogs

Overview of Proteinuria (Excessive Protein in Urine) in Dogs

Proteinuria, in dogs, 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.

Diagnosis of Proteinuria in Dogs

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 of Proteinuria in Dogs

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.

In-depth Information on Proteinuria in Dogs

The kidneys are responsible for maintaining fluid and mineral balance in the body. Water and essential molecules are reabsorbed from the tubules and the remaining waste products are excreted as urine. Certain molecules, such as proteins, are kept in the blood stream by the filtering units of the kidney, the glomerulus. Glomeruli are small tufts of capillary blood vessels that act as a sieve, allowing small substances to pass through while keeping larger substances (protein, blood cells) in the bloodstream.

When glomeruli are damaged they can become leaky. When red and white blood cells and proteins are loss through the kidney it is a condition called glomerulonephritis. The excessive loss of protein through the glomerulus is called proteinuria.

Glomerular proteinuria may be divided into selective and nonselective proteinuria. With selective glomerular proteinuria large amounts of albumin are lost through the glomerulus. It results from a number of disorders but primarily from immune-mediated diseases and amyloidosis. The causes of nonselective glomerular proteinuria are the same as with selective glomerular proteinuria but results in a more severe proteinuria with loss of globulins, fibrinogen, antithrombin III (which is responsible for preventing blood clots) as well as albumin.

Diagnosis In-depth

• When a positive reaction for protein is detected on a routine urinalysis, the urine sediment should be evaluated
• If pyuria (white blood cells in urine) is present then culture the urine to determine which type of bacteria is present
• If blood is present in the urine look for causes of hemorrhage
• If positive for blood but no intact red cells are seen consider hemolysis (red blood cell destruction). A positive blood test can also indicate hemoglobin or myoglobin in the urine
• If casts of kidney tubules are seen, a disease of the kidney should be considered
• Perform a urine protein/creatinine (U P/C) ratio. Measures the amount of protein and creatinine in a single sample. The U P/C of a single random urine sample from dogs with normal and abnormal glomerular function correlates with a 24 hour collection determination. A ratio greater than 1 is considered abnormal.
• A 24 hour total urine protein quantification can also be performed by collecting all the animal’s urine over a 24 hour period. In general, urine protein excretion values less than 30 mg/kg/day can be considered normal for cats and dogs.
• Once proteinuria is confirmed obtain a complete blood count (CBC) and serum biochemistry profile
• If the blood albumin level is decreased suspect glomerular disease
• Blood pressure determination is important to identify systemic hypertension (high blood pressure)
• Clotting profile and antithrombin III levels are performed to determine if the pet is at risk for bleeding problems or at an excessive risk for developing a thromboembolus (blood clot)
• Kidney biopsy ultimately is needed to identify glomerulonephritis from amyloidosis

For more information, please read glomerulonephritis.

Treatment In-depth

The treatment of proteinuria depends on the the underlying cause.