Downeast Dog News
https://downeastdognews.villagesoup.com/p/1886924

Canine Kidney Failure: “What Now?”

Part I
By Dr. Gail Mason, DVM, MA, DACVIM | Apr 01, 2021

The diagnosis of "kidney failure" can come as a shock to many owners. The symptoms may be very subtle and prolonged in onset. Veterinarians prefer a less dramatic term referred to as “renal insufficiency” or chronic kidney disease (CKD), as it is generally not an all or nothing diagnosis. The term kidney failure or renal insufficiency denotes that the kidneys are not doing at least some of the tasks that they are supposed to do. It is important to note that an early diagnosis with appropriate intervention can significantly improve and extend your dog’s life for months to even years.

The normal kidney is composed of microscopic units referred to as nephrons. Each kidney contains thousands of nephrons which are individual filtering units. In a young dog, not all of the nephrons are working all of the time as some are held in "reserve. “As the dog ages and/or if the kidneys are damaged, some nephrons die off and other resting nephrons are called in off the bench to take over. Eventually, the kidneys run out of spare nephrons and any further damage to the kidneys will result in early signs of renal insufficiency. When the nephron loss is greater than 2/3 of the total number, the dog will no longer be able to produce a concentrated urine. When 75% of the nephrons have been lost, the patient will experience a rise in a waste product known as “creatinine”, as measured in the bloodstream.

What Do Kidneys Do?

The kidneys act as a complex filtering system that removes metabolic waste that is generated from the breakdown of food, old cells, toxins or poisons, and many drugs that are given for the treatment of other diseases. The wastes are removed with water as urine. The kidneys also act as a filter to keep beneficial substances within the blood stream. They regulate the amount of water in the blood by excreting extra water (when intake exceeds the need), or conserving water (to prevent dehydration) by making the urine more concentrated. The kidneys also have an important role in regulating blood pressure and electrolyte balance within the body. If those aren’t enough tasks, the kidneys are also responsible for controlling calcium and phosphorous balance within the body plus producing a hormone called “erythropoietin” which influences the bone marrow’s production of red blood cells. No wonder why dogs have two of them!

Symptoms of Kidney Disease

Because the kidney’s nephron losses prevent it from conserving water, the first symptoms are generally increased thirst and increased urinations. These symptoms are not specific, however, as they can also be present in other common canine diseases such as diabetes mellitus, kidney infection (pyelonephritis), and Cushing’s disease. As renal insufficiency progresses, you may notice that your dog has a decreased appetite, intermittent nausea, halitosis, weight loss, and gastroenteritis which result from the increased toxic waste within the dog’s bloodstream.

Diagnosis

Your veterinarian may start with evaluation of a complete blood count (CBC), which evaluates red blood cell and white blood cell counts and may show evidence of anemia or infection. A blood chemistry panel measures components in the blood that indicate how well the internal organs are functioning. In particular, the blood urea nitrogen (BUN), creatinine, phosphorus, and SDMA are important renal values. The greater the degree of renal insufficiency, the greater the rise in these numerical values are.

A urinalysis is one of the most important parameters measured to assess renal function (as well as potential causes of renal dysfunction). One of the terms that you may hear about is "urine specific gravity." This refers to how concentrated a urine sample is. Water has a specific gravity of 1.000. A dilute sample has a specific gravity less than that of 1.020 (and often less than 1.010). A concentrated urine sample would have a specific gravity greater than 1.030. A failing kidney, by definition, cannot make a concentrated urine and the patient must drink more water to compensate. A urine sample is also analyzed for potential signs of infection (which can cause temporary and perhaps reversible renal insufficiency), cellular injury, and protein loss through the kidneys. Frequently, a urine culture is submitted to detect bacterial infection that may not be visible on a dilute urine sample. This is an important step, as if infection is part of the cause of the renal insufficiency, effective treatment may improve the overall function. If the urine contains an excessive amount of protein (highly conserved by normal kidneys), it can be quantitated utilizing a test called a "urine protein: creatinine ratio." Excessive protein loss through the kidneys can result in protein deficiency, hypertension, and blood clotting abnormalities. Additional diagnostics may include imaging by radiographs (x-rays) and or an abdominal ultrasound to investigate the renal system in more detail. As frightening as all this information may sound, effective management of CKD is possible. Next time, we will discuss treatment and monitoring of patients with CKD.