Almost Everything You Need to Know About
Chronic Renal Failure
Chronic Renal Failure
But Might Be Afraid to Ask
First - let's get some definitions down:
Chronic: long term.
Renal: kidney. (we use them interchangeably)
Failure: the inability to perform a task adequately.
Chronic renal failure (CRF), also called chronic kidney failure, refers to the situation where the kidneys have not been able to perform at least one of their many tasks adequately for some time (months to years). Many doctors opt for the term chronic renal insufficiency, as many cases can be treated successfully and can look forward to months or often years of quality life, while failure connotes negativity. In addition, at this time we do not usually do dialysis with pets, but there are some programs for kidney transplants available in cats.
Kidneys: two bean-shaped organs present in our abdominal cavity that make urine and a whole lot more! The kidneys are made of thousands of tiny filtration units called nephrons. Once a nephron is destroyed by a disease, it is not replaced; the number of nephrons we have has to last a lifetime (or at least quite a few need to last a lifetime-we do have extras).
Many people have no idea what our kidneys do for us beyond that they have something to do with urine production. In fact, the kidneys are involved in conservation of water, stimulating red blood cell production, regulating blood pressure, balancing salts, activating Vitamin D, and more. Any of these functions may be failing in the renal failure patient.
The kidneys remove toxic wastes from our bodies and when these substances cannot be adequately removed, we develop excess thirst, nausea, pain, weakness, appetite loss, intestinal bleeding, even seizures. Our goal in early stage patients is to postpone or even fully prevent the development of uremia. Our goal in later stage patients is to resolve the uremia and bring the patient back to an earlier stage of disease.
If the pet is still making plenty of urine, how can there be kidney failure?
In chronic kidney failure, urine is usually produced in excessive quantities. What the kidneys are failing to do is conserve water and they fail to make concentrated urine. The body produces numerous toxins as it goes through its daily tasks. These toxins circulate to the kidneys where they are filtered out and urinated away. 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.
When the kidneys fail, they lose their ability to concentrate urine and more water is required to excrete the same amount of toxin. This usually starts to happen when about 2/3 of the nephrons are no longer working. The animal will begin to drink more and more to provide the failing kidneys with enough water. Eventually, the animal cannot drink enough and toxin levels begin to rise. At first owners might notice only that they are filling the water bowl more often, or the litter box is wetter, or that the dog has to go out more often or is having accidents. Later the pet owner might notice weight loss, listlessness, nausea, constipation, and poor appetite.
Fortunately, we have many extra nephrons, so many extra that overall kidney function does not fall behind until we are down to about 1/4 of our original number of nephrons.
Nephrons can be destroyed quickly or slowly. Usually, by the time less than 1/4 of our original nephrons are left, whatever the inciting disease process was is long gone and there is no way to tell what happened. All we can do is make the kidney workload easier by making up for the kidney’s inadequate performance with medication or supplements. Hopefully, we can also slow the progression of the failure. Therapy is highly individual depending on which jobs the kidneys are having trouble doing.
Azotemia: the condition where toxins have built up in the bloodstream and lab tests are definitely abnormal. It does not necessarily mean the patient is experiencing reduced life quality as a result of these abnormal lab findings.
Uremia means that the patient is experiencing uremic poisoning. In other words, not only are the tests abnormal but the patient is feeling the effects of the toxic build up.
Therapy: Our goal in treatment is to prevent, postpone, or resolve uremia. Resolving azotemia may not be realistic. In most cases, by the time the diagnosis of kidney failure has been made, the initial disease that started the kidneys on their path to failure is long gone, leaving a progressive loss of function to march unrelentingly onward. Our goal is to stop that march, and get to a stage where the patient does not feel the consequences of the disease. We cannot make failed kidneys become normal again, but we may be able to re-balance our patient’s metabolism so that he or she feels as though we did. What makes a case hopeless or hopeful depends on the patient’s ability to respond to therapy nearly as much as it depends on the stage at which the condition is discovered. See suggestions after each of the lab parameters we monitor.
Lessons in Lab Work:Let’s begin with some of the relevant lab values that come up in the course of screening a pet’s kidney function. Your veterinarian may also recommend other tests besides these, such as urine sediment and/or culture if there is a chance that there is a urinary tract infection present as well. It is helpful to familiarize yourself with these terms so you can understand what your veterinarian is monitoring:
Urine Specific Gravity: One of the kidney’s most important jobs is the conservation of the body’s water. The kidney must excrete the toxic by-products created by the body’s metabolism but it will want to do so in the least amount of water possible. The healthy kidney is able to make very concentrated urine.
When we analyze a urine sample, one of the most important parameters is the specific gravity. This is a measure of how concentrated a urine sample is. Water has a specific gravity of 1.000. A dilute urine sample has a specific gravity less that 1.020. A concentrated urine sample would have a specific gravity over 1.030 (dogs) or 1.040 (cats). A failing kidney by definition cannot make concentrated urine and the patient must drink excessively to get enough water to excrete the day’s toxic load. At certain times of the day our urine is more concentrated than others-our first morning urine tends to be our most concentrated of the day since we usually don’t drink much at night if we are in good shape, but if we just had a big drink, our next urine will be more dilute.
Blood Urea Nitrogen (BUN): This is a protein metabolite excreted by the kidney (it is one of the toxins we are concerned about, though it may be more of a marker for other toxins that are less easily measured). In a normal animal, the BUN is around 25 mg/dl (milligram per deciliter). Often at the time of diagnosis, BUN is well over 150, 200, or even 300. We’d like to keep the BUN no more than 60 to 80 mg/dl. BUN is influenced by dietary protein (including the patient’s own blood that has bled into the intestine).
Creatinine: This is another protein metabolite (though this one is less dependent on dietary protein intake than is BUN). A normal creatinine is less than 1.4 mg/dl, certainly less than 2.0. Patients begin to feel sick when values meet or exceed 5.0 so we try to keep the value at 4.5 or less. BUN and creatinine will be tracked (as will several other parameters) over time and in response to different treatments.
Therapy to address fluid loss and azotemia (elevated BUN and Creatinine):
First, is giving fluids to help keep the pet hydrated, to optimize blood flow to the kidneys, and to help flush out toxins from the blood stream. Also, we institute dietary management to give the body proteins that it can utilize best and to decrease excess protein metabolites. Additionally, we use gastrointestinal medications such as stomach acid blockers of various kinds, appetite stimulants, and anti-nausea medications since kidney failure leads to excess stomach acid secretion, and nausea.
Phosphorus: The calcium/phosphorus balance becomes deranged in kidney failure due to hormone changes as well as the inability of the failing kidney to excrete phosphorus. If calcium and phosphorus levels become too high, the soft tissues of the animal's body will become more like bone with deposits of mineral in them that are inflammatory, uncomfortable, and often cause intestinal bleeding. The bones will weaken as well, in some cases actually becoming rubbery. Keeping phosphorus levels in the low normal range has been correlated with improved survival.
Therapy for excess phosphorous: Phosphorous binders added to the diet, and if we can get the phosphorous and calcium down low enough (so that if you multiply the numbers you get for each mineral the answer should be less than 60), a medication called calcitriol may slow further kidney decline.
Potassium: The failing kidney is unable to conserve potassium efficiently and supplementation may be needed. The sign of hypokalemia (the scientific name for low blood potassium) is weakness, especially drooping of the head and neck.
Therapy for low potassium is a potassium supplement.
Packed Cell Volume / Hematocrit: This is a measure of red blood cell amount. More literally it represents the percentage of the blood made up by red blood cells. The hormone which stimulates the production of red blood cells is made by the kidney. The failing kidney does not make this hormone in normal amounts leading to a reduction in red blood cells (anemia), in turn leading to weakness, poor appetite, and overall poor life quality.
Therapy for anemia in kidney failure is using an injectable form of the hormone that stimulates bone marrow to make red blood cells.
Blood Pressure: Blood pressure is important to monitor in kidney patients as there is a tendency for hypertension (high blood pressure) to develop in kidney failure.
Therapy consists of medication to lower blood pressure and certain medications work better in certain species.
Thyroid Hormone: In our cat patients, it is important to screen thyroid hormone level as hyperthyroidism can lead to high blood pressure and kidney damage.
Therapy involves stopping excess thyroid hormone production via one of several ways: a medication usually given orally, dietary management, surgery to remove the overactive tissue, or radioactive iodine treatment.
Urinary Protein: One of the functions of the kidney is to prevent loss of the body’s blood proteins. The kidney’s filtering mechanism that enables it to remove toxins is designed to leave larger molecules (such as proteins) inside the body where they belong. But if holes develop in the filter, protein can be lost. If this complication cannot be controlled, survival time is dramatically shortened.
Therapy consists of using a medication that is used in heart disease, called an ACE inhibitor. These medications also reduce blood pressure somewhat and decrease protein excretion in some patients.
REMEMBER, While all of this information may seem overwhelming and insurmountable, remember that many cases of kidney failure can be treated successfully and patients can look forward to months or often years of quality life with management!
Dr. Dana Lewis
Dr. Dana assists families with Pet Hospice and In Home Euthanasia in the Raleigh North Carolina area (Raleigh, Durham, Chapel Hill and the greater Triangle, as well as Wake, Durham, Orange, and Chatham counties.)