One of the more frustrating and unfortunately common diseases we see in veterinary medicine is kidney disease. Kidney disease in and of itself can mean many things; kidney stones, infections, cancer, or failure. With this post I will do my best to inform you of the ins and outs of kidney (renal) failure. In a subsequent post I will proceed to address the steps we can take to manage kidney failure in hopes of providing our beloved fur babies great quality of life for as long as possible.
Before we discuss the signs of kidney failure, it is important to understand the importance of these paired “bean shaped” organs. Many people have no idea what our kidneys do beyond having something to do with urine production. In fact, the kidneys are involved in so much more! The kidneys are responsible for conservation of water, stimulating red blood cell production, regulating blood pressure, balancing salts, activating Vitamin D, and more.
The causes of kidney failure are vast in number. Some of these causes include severe or prolonged bacterial/viral infections, toxin exposure, cysts or masses in the kidneys, autoimmune disease (where the pet’s immune system reacts against its own kidneys), urinary obstructions, and so on. Unfortunately kidneys do not have the ability to heal the way some organs do, so when they become damaged the effects are typically irreversible.
Warning Signs and Diagnosis
One of the first symptoms owners observe in a patient with kidney disease is increased thirst and urination. This is due to the kidneys’ inability to concentrate urine appropriately (discussed later). Other symptoms to look out for include lethargy, loss of appetite, weight loss, dehydration, vomiting, and even foul breath. Since the above listed symptoms are also frequently associated with other disease processes it is important to have a full medical workup including blood work, and a urinalysis (examination of a urine sample) to differentiate renal failure from other diseases.
What do these values mean?
The most common findings we see on blood work would be increases of BUN and creatinine. Cats and dogs only need 25% of their paired kidney function (or half of one kidney) in order for routine blood work to appear “normal”. Other common laboratory abnormalities include dilute urine, elevation in blood phosphorus, decrease in blood potassium, anemia, and high blood pressure (hypertension).
Blood Urea Nitrogen (BUN): This is a protein metabolite excreted by the kidney. When this value is on the rise it can be an early warning sign for kidney troubles. However, an increase in BUN can be seen if a patient is on a high protein diet, dehydrated, or even due to loss of muscle mass as a patient ages. Therefore it is important to understand that an increase of BUN does not always indicate a life threatening condition, but when combined with other laboratory abnormalities it may support a diagnosis of kidney failure.
Creatinine: This is another protein metabolite (though less influenced by other factors as BUN). Creatinine is excreted almost exclusively by the kidney and therefore this value is a great indicator of glomerular filtration or “good” kidney function.
Urine Specific Gravity (U.S.G.): When we analyze a urine sample, one of the most important parameters we assess is the specific gravity. Specific gravity is a measure of how concentrated a urine sample is. In chronic kidney failure, urine is usually produced in excess due to the kidneys’ inability to conserve water. The body produces numerous toxins as it goes through its daily tasks. These toxins circulate to the kidneys where they are filtered out of the blood and urinated away. The toxins are essentially what concentrates the urine. An efficient kidney can make highly-concentrated urine so that a large amount of toxin can be excreted in a relatively small amount of water, but when the kidneys don’t function properly higher volumes of urine are produced in attempts to excrete these toxins from the body. U.S.G. can be affected by the time of day and even your pet’s recent water intake so it is important to keep this in mind if your pet’s urine appears dilute.
Potassium: Most of the potassium in the body is stored inside cells, allowing for normal cellular function. Low levels of potassium can therefore dramatically affect the functionality of the tissues (including muscle) in the body. Due to the decrease in cellular function one of the key signs of hypokalemia (scientific name for low blood potassium) is weakness.
Packed Cell Volume / Hematocrit / Red Blood Cell Count: As kidney failure progresses one of the additional changes we may see on blood work would be an indication of anemia. Anemia is a condition marked by a deficiency of red blood cells (RBCs) or hemoglobin. Hemoglobin is a protein found inside RBCs that is essential for carrying oxygen. The hormone which stimulates the production of RBCs (erythropoietin) is made by the kidney. If the kidneys are unable to produce this hormone we see a reduction in overall RBCs. If the body’s organs don’t get the oxygen they need, they function below healthy levels resulting in weakness, and overall poor life quality.
High Blood Pressure (hypertension): Secondary hypertension is seen in ~20% of dogs and cats diagnosed with kidney failure. The mechanisms by which renal failure causes hypertension in dogs and cats have not been adequately studied, but theories range from imbalances in electrolytes, reduced renal blood flow, hormone level disturbances, etc. What we do know is that prolonged hypertension may result in further organ damage to the kidneys, irreversible damage to the eyes, and cardiovascular system.
If your pet is exhibiting any of these abnormalities during diagnostic testing, we recommend that these abnormalities continue to be tracked over time in hopes of gauging the progression of disease and response to treatment/management.
If you made it this far I applaud your desire to learn more about an all too common disease we encounter in veterinary medicine. I hope you will return for my follow-up where I will discuss the therapeutic options available for any patient afflicted with kidney disease.
REMEMBER, While all of this information may seem overwhelming and insurmountable, know that many cases of kidney failure can be managed successfully and patients can look forward to months or often years of quality life!