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:
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:
Animals with glomerular proteinuria are described as having glomerulonephritis or a glomerulonephropathy.
Diagnosis of Proteinuria in Dogs
Diagnostic tests needed to identify proteinuria include:
Treatment of Proteinuria in Dogs
There are three basic treatment objectives:
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.
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.
For more information, please read glomerulonephritis.
The treatment of proteinuria depends on the the underlying cause.