Glomerular disease occurs quite commonly in dogs. It affects purebreds and mixed-breeds alike, and can be an inherited disorder in Shar Peis, Soft Coated Wheaten Terriers, Bull Terriers, Dalmatians, Samoyeds, Bernese Mountain Dogs, Doberman Pinschers, Newfoundlands, and English Cocker Spaniels.
Veterinarians use a number of different terms interchangeably when describing “glomerular disease”.
Here is a sampling of those most commonly used:
- Protein losing nephropathy
Each kidney contains millions of glomeruli, microscopic filtration units that interface with the blood vessels that supply the kidneys. I like to think of a glomerulus as a tiny sieve or colander because the size of its pores dictates which substances within the blood are allowed to enter into the fluid that ultimately becomes urine. Normal glomeruli do not allow larger protein molecules such as albumin to pass into the urine.
The most common means by which glomeruli are damaged include:
- Inflammation, particularly that which is immune mediated (autoimmune) in nature
- A form of scarring referred to as glomerulosclerosis
- Persistent high pressure blood flow to the kidneys (e.g., elevated blood pressure)
- Deposition of a protein called amyloid (this is referred to as amyloidosis)
When glomeruli are damaged, they become “leakier,” thus allowing larger protein molecules to filter into the urine.
Persistent proteinuria (increased protein within the urine) is a hallmark characteristic of glomerular disease.
Glomerular damage may be present at the very earliest onset of kidney disease, well before there are other measurable laboratory changes or symptoms typically associated with kidney damage. Moreover, compared to dogs with kidney disease and no proteinuria, those with glomerular damage are far more likely to develop significant illness and/or death as a result of their kidney disorder. In other words, glomerular disease, particularly when left untreated, hastens the progression of kidney failure.
Glomerular damage can arise as a primary disease process, or it can occur secondary to another underlying disease.
Diseases commonly associated with secondary glomerular injury include:
- Heartworm disease
- Infectious diseases (bacterial, fungal, tick-borne)
- Cancerous diseases
- Immune mediated (autoimmune) diseases
Symptoms of glomerular disease
In and of itself, protein loss in the urine does not cause any symptoms. Therefore, many dogs with glomerular disease, particularly early on, appear completely normal. When symptoms do arise, they are usually related to one or more of the following:
- The underlying disease process causing the glomerular damage (see the list above)
- Kidney failure
- Complications associated with glomerular damage (high blood pressure, decreased protein in the bloodstream, blood clot formation)
- Loss of appetite
- Increased thirst and urine output
- Weight loss
- Halitosis (bad breath)
Documentation of excessive protein in the urine
There are four different laboratory tests that can be used to assess protein within the urine. They include:
- Urinalysis: This provides “semi-quantitative results.” This means that a positive test result gives only a rough idea of how much protein is in the urine. The urinalysis is a very useful first screening test, but it is fraught with false positive results. Additionally, it is not always sensitive enough to detect the very earliest stages of glomerular damage. For these reasons, follow up testing via another methodology (see below) should be performed, either when the urinalysis is positive for protein or when the urinalysis is negative for protein but glomerular damage is suspected (e.g., dogs of breeds with inherited forms of glomerular disease).
- Urine protein to creatinine ratio: This test helps quantify the amount of protein in the urine. This accomplishes two things. It verifies whether the amount of protein in a urine sample is normal or increased. Secondly, it establishes a baseline to which future samples can be compared. This helps in the monitoring of disease progression.
- Microalbuminuria testing: This test detects very small amounts of a protein called albumin within the urine, even before proteinuria can be documented via a urinalysis. As such a sensitive test, it is recommended in the following situations:
- The results of other screening tests for proteinuria are negative in a dog with a serious illness, particularly one known to be associated with glomerular disease (see the causes of glomerular disease above).
- As a general health screening test in middle-aged and older dogs.
- As an early-age screening test for dogs with a possible inherited predisposition for glomerular disease.
- 24-hour urine protein quantification: Back when I was a pup (before urine protein to creatinine ratios and microalbuminuria testing were available) we would house a dog in a “metabolic cage” or place a urinary catheter so as to collect every drop of urine produced over a 24-hour period. The amount of protein in this duration of urine was then measured. This methodology was a pain-in-the-you-know-what for everyone involved, particularly the poor dog. Thank goodness, such testing is now considered antiquated and is rarely if ever used.
Diagnosing glomerular disease
If a dog demonstrates persistent proteinuria (repeatable on multiple tests over the course of a few weeks), a battery of tests is typically recommended to rule out non-glomerular causes of excess protein within the urine such as urinary tract infection, stones, or bleeding. This testing typically includes the following:
- Complete blood cell count (CBC)
- Blood chemistry profile
- Urine culture
- Abdominal ultrasound or x-rays
- Heartworm testing
- Chest x-rays
- Abdominal ultrasound
- Specific screening tests for infectious diseases
This can be accomplished via surgery, laparoscopy, or with ultrasound guidance. Whichever methodology is used, collection of a kidney biopsy has the potential to cause significant complications. Thoughtful discussion with a veterinarian about risks and benefits should always precede a kidney biopsy.
Complications commonly caused by glomerular disease
As if glomerular disease isn’t enough to worry about, it is capable of causing a number of serious secondary issues including:
- Hypertension (high blood pressure): Can cause damage in heart, kidneys, brain, and/or retinas; hypertension promotes proteinuria
- Hypercoagulability (an increased propensity to form blood clots): Thromboembolism (blood clot) formation can occur within any organ
- Kidney failure
Treatment of glomerular disease
There are four primary goals when treating canine glomerular disease. How they are implemented will depend, in part, on the dog’s kidney function and degree of proteinuria.
1. Identify and eliminate the underlying cause of the glomerular damage
Doing so may resolve the proteinuria altogether (the best outcome possible). For example, successful treatment of heartworm disease often eliminates the associated glomerular damage. Unfortunately, in many cases, the underlying cause of the glomerular disease cannot be identified or successfully eliminated.
2. Attempt to lessen the degree of proteinuria
Doing so is the best bet for slowing the progression of kidney damage and other complications associated with glomerular disease. The mainstays of such therapy include:
- Feeding a diet that is low in quantity, but high in quality in terms of protein content: This decreases the amount of protein filtered by the kidneys.
- Supplementation with omega-3 fatty acids: Their anti-inflammatory effects are thought to be responsible for decreasing proteinuria.
- Administration of an angiotensin-converting-enzyme inhibitor drug (enalapril, benazepril): Alters microscopic blood flow at the level of the kidneys.
3. Treatment of glomerular disease complications
- Immunosuppressive drugs: Suppression of the immune system may help diminish glomerular inflammation.
Examples of such treatments include administration of medications to control high blood pressure, anticoagulant therapy to help prevent blood clot formation, and daily subcutaneous fluids to manage kidney failure.
4. Follow up monitoring
Once the diagnosis of glomerular disease is made and treatment is instituted, there will be a need for ongoing monitoring. The results of such monitoring will direct how the dog’s therapy should be adjusted. A typical follow up veterinary visit for a dog with glomerular disease would include:
- Discussion of how the dog is doing at home
- A thorough physical examination
- Blood pressure measurement
- Blood testing to evaluate kidney function
- Urine protein to creatinine ratio
The earlier glomerular disease is detected and managed, the greater the likelihood of deterring a negative outcome. Left unchecked, glomerular disease is known to increase the severity and progression of kidney failure.
Canine glomerular disease is often associated with kidney failure which may progress very slowly, very quickly, or anything in between. Some dogs live for several years with glomerular disease. The likelihood of such an outcome is far greater with appropriate treatment and monitoring.
Dogs with severe glomerular disease can progress to a condition that is referred to as nephrotic syndrome. This is characterized by the following four abnormalities:
- Excess protein loss in the urine
- Decreased protein (specifically albumin) within the blood stream
- Elevated blood cholesterol level
- Presence of edema (accumulation of watery fluid under the skin or within body cavities)
Nephrotic syndrome represents an advanced stage of glomerular disease.
In addition to the treatment options mentioned above, measures to manage the edema (fluid drainage, specific medications) may be warranted.
Have you had any experience with glomerular disease in your dogs?
Diplomate, American College of Veterinary Internal Medicine
Author of Speaking for Spot: Be the Advocate Your Dog Needs to Live a Happy, Healthy, Longer Life
Author of Your Dog’s Best Health: A Dozen Reasonable Things to Expect From Your Vet
Recipient, Leo K. Bustad Companion Animal Veterinarian of the Year Award
Recipient, American Animal Hospital Association Animal Welfare and Humane Ethics Award
Recipient, Dog Writers Association of America Award for Best Blog
Recipient, Eukanuba Canine Health Award
Recipient, AKC Club Publication Excellence Award
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