Written by: Alexa Waltz
The kidneys are extremely important players in the game of keeping the bodies of humans and animals healthy. Like humans, dogs are born with two kidneys that are primarily responsible for excreting wastes and toxins from the bloodstream and maintaining fluid and electrolyte balances within the body. Kidney disease goes by many other names like “renal failure”, “renal insufficiency”, “kidney damage”, “kidney insufficiency”, “kidney injury”, and “kidney failure”. All of these names imply that the kidneys are struggling to carry out their normal functions to some degree. Kidney disease can also be further described as “acute” (happening suddenly or quickly) or “chronic” (happening slowly over time).
So many questions revolve around the diagnosis of kidney failure in dogs, and it can be very scary and confusing for pet parents. How can I tell if my dog has kidney disease? What would cause my dog’s kidneys to fail? How does kidney disease affect the long-term health of my dog? Recognizing what the kidneys do for the body is key to understanding, diagnosing, and treating kidney disease.
What Do the Kidneys Do?
Everyone knows at least one important thing about the kidneys: they make urine! The kidneys are made up of millions of little tiny cellular units called nephrons. As blood flows through the kidneys, each nephron is designed to regulate what stays in and what is filtered out of the blood and into the urine – be it waste products from metabolism, toxins, electrolytes, and water. The healthy nephron uses a system of highly specialized cellular channels, pumps, gates, gradients, sensors, receptors, and hormones to filter unnecessary materials from the blood without losing what is valuable – it is really an incredible process! For example, during times of dehydration in dogs, healthy kidneys will conserve water in the bloodstream and produce very concentrated urine (a dark yellow color) and in times of hydration, they will excrete that excess fluid and make a very dilute urine (a light yellow/clear color).
However, the kidneys do much more than just make pee! In fact, the healthy function of other organs hinges on the kidneys keeping everything balanced. Here is a brief summary of how the kidneys are incredible workhorses for the body:
– Maintain blood pressure
– Filter wastes and toxins
– Conserve or excrete water
– Regulate blood electrolyte and mineral levels (especially sodium, potassium, phosphorus, and calcium)
– Synthesize erythropoietin to stimulate red blood cell production
– Conserve important blood proteins
– Maintain blood pH balance
How Do Kidneys Become Damaged?
Being the fragile filter of the body, unfortunately, the kidneys are in a highly vulnerable position and can be damaged by a variety of different types of medical problems. Here is a list of the most common causes of acute (sudden) and chronic (slowly over time) kidney failure:
– Ingesting Toxins (grapes, antifreeze, over-the-counter human NSAIDS like Ibuprofen)
– Infections and Inflammation (Lyme disease, leptospirosis, pancreatitis)
– Dehydration, Heatstroke
– Aging (kidneys “wear out” over time)
– High blood pressure
– Kidney stones
– Diabetes (Link: diabetes)
– Periodontal disease (Link: periodontal disease)
– Genetic and developmental abnormalities
The kidneys have significant reserve and are excellent at compensating, even as some nephrons wear out or become damaged and nonfunctional. In fact, changes in your dog’s lab work won’t be apparent until at least 2/3 of those millions of nephrons become compromised! Unfortunately, when damaged beyond repair, the kidney is an organ that does not regenerate itself. This is why it’s essential to start treatment for kidney disease and investigate the underlying cause of kidney damage as soon as a problem is detected.
Acute Renal Failure happens very quickly – usually over a matter of hours to days — with the sudden loss of kidney function. Infections, toxin ingestion, and severe dehydration/heat stroke are often causes of acute renal failure. With appropriate emergency treatment, acute kidney failure may be reversible! Aggressive treatment may help the kidneys regain some or all of their function again depending on the cause and the treatment received. Without treatment, acute renal failure can be fatal.
Chronic Renal Disease, or chronic renal failure, is a more gradual process taking place over months and years. This means that over a long period of time at least ⅔ of the kidney’s nephrons have become damaged beyond repair. The kidney loses the ability to filter waste products, concentrate the urine, regulate blood pressure, balance electrolytes and minerals, and stimulate the production of red blood cells. They may also be leaking protein into the urine because those specialized filters just do not work anymore. Kidney function greatly affects other organs too, like the heart, GI tract, and eyes, so depending on the actions taken to support the failing kidneys, dogs can have a variety of concurrent issues arise.
How Can We Tell if the Kidneys Are Damaged?
Refilling that water bowl more than normal? If your dog is drinking more and in turn having to pee more, this is a commonly recognized symptom of chronic kidney disease. Increased thirst and urination closely resemble the symptoms of diabetes as well, which is another serious health condition. Along with changes in water consumption and urination, keep an eye out for weight loss, decreased appetite, low energy, weakness, vomiting, and diarrhea too.
AskVet Tip: Acute kidney failure can cause your dog to feel very sick and also suddenly decrease its urine production. This happens because the kidney tissue has been so severely injured that the kidneys have basically “closed up shop” and are not working at all! This is an extremely dangerous and life-threatening situation that needs immediate emergency care. Chronic end-stage kidney failure, when the kidneys have very little functional capacity left, may be accompanied by bad/sweet breath and vomiting blood or black flecks of digested blood. This is due to the buildup of harmful toxins in the bloodstream that cause ulcers in the mouth, stomach, and intestines. Your dog also may have lost a significant amount of weight and may not be eating much at all.
Blood and Urine Testing, Imaging, and Blood Pressure Readings
Sometimes kidney insufficiency is detected on lab work well before any of the above physical signs develop, and early detection is a great thing! This is one of the many reasons that a blood test and urine test are recommended routinely for dogs and cats even if they are not showing signs of being sick – to catch diseases early in their progression! This way, we can initiate some protective treatment early to preserve kidney function for as long as possible.
If you suspect your dog may be showing signs of kidney disease, your vet will perform a physical exam first, looking for signs of dehydration, checking bladder size, heart and respiratory rate, etc. Next, they will likely recommend a urinalysis (urine test) and blood testing as this is the best way to check on how her internal organs are functioning. The urine tests will show if there is infection or inflammation present, if the kidneys are concentrating the urine appropriately, and if there is any other evidence of kidney damage in the urine sample. The blood tests will have several kidney function markers (BUN, Creatinine, SDMA) that become elevated when nephrons are damaged and not filtering correctly. Protein levels, blood electrolytes like sodium and potassium, and mineral levels of calcium and phosphorus are also important in determining the degree of kidney damage. Anemia, or low red blood cell count, is an important observation too. Additional testing to further examine aspects of the blood or urine may also be recommended for your dog depending on the screening test results. X-rays and ultrasound of the kidneys and abdominal organs also help to examine the kidney size and appearance, check for stones in the urinary tract, visualize tumors, and scan for abnormalities in other organs.
Lastly, measuring a dog’s blood pressure is also very important. Kidney disease can cause high blood pressure AND high blood pressure can further damage the kidneys! It is essential to obtain as much information as possible in order to tailor your dog’s treatments to preserve kidney function.
AskVet Tip: Kidney disease is graded on a scale from 1-4, 1 being mild and 4 being severe disease. The results of diagnostic testing help to put the puzzle pieces together and determine the stage of kidney disease. At that time, the doctor and pet parent discuss the prognosis, treatments, and long-term expectations together.
What About Long-Term Health?
The diagnosis of kidney disease does not necessarily mean doom and gloom for your dog! Your dog’s journey with kidney disease highly depends on the stage, initial cause, degree of damage, progression, and treatments. If the issue is detected very early and protective measures are put in place, it is possible for dogs to stabilize and live for many years without showing outward signs of having an issue.
It is important that dogs diagnosed with kidney disease follow up with their veterinarian every 6-12 months as recommended. This allows their vet to keep a close eye on any progression of kidney damage, and to determine when to tweak your dog’s therapy or add further treatments. It is very possible for dogs with kidney disease to live happy and comfortable lives!
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Alexa Waltz, DVM
Dr. Waltz was raised near the beaches of Southern California but has spent her adult life living all over the beautiful United States while serving in the military and as a military spouse. She left California for the first time to pursue a career as a veterinarian at Louisiana State University School of Veterinary Medicine and graduated as a Doctor of Veterinary Medicine in 2006. She was accepted into the US Army Health Professionals Scholarship Program during vet school and upon graduation spent her military years as a veterinarian in San Diego working for the US Marine Corps and US Navy Military Working Dog programs as well as caring for pets of service members. After her military service, she became a civilian veterinarian and continued as a small animal general practitioner at clinics in California, Rhode Island, Colorado, and Maryland. Dr Waltz loves to see her “in person” patients just as much as communicating with and assisting pet parents virtually on AskVet. Dr Waltz is also a Mom to 3 humans, 2 guinea pigs, and 1 Australian Shepherd and in her spare time she loves traveling, adventures, exercising, and doing just about anything out in nature!