The term kidney failure, or kidney insufficiency, simply means that the kidneys are not able to do at least some of the tasks they are supposed to do as well as they are supposed to do them. Kidney insufficiency is one of those conditions where early intervention can make a big difference and normal life quality can be maintained for months or even years.
A pet with insufficient kidney function will not be able to make a concentrated urine and will need to drink extra water to process the body's waste chemicals. For this reason, excessive water consumption and increased urine output are typically the first clinical signs that owners will notice.
The kidneys remove our metabolic wastes from the blood. If there is inadequate circulation going through the kidneys or if there is not enough functioning kidney to handle the waste load, toxins will build up in the bloodstream. When these toxins exceed the normal range, a condition called azotemia exists. If the toxins build up to a level where the patient actually feels sick, a condition called uremia exists. The goal of treating kidney insufficiency is to keep our azotemic patient below the uremia level, so they will feel pretty normal and maintain good life quality.
We diagnose kidney disease and monitor kidney function by performing blood and urine tests.
Urine testing: 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 concentrated urine sample should have a specific gravity over 1.030 or 1.040. A failing kidney by definition cannot make a concentrated urine and the patient must drink excessively to get enough water to excrete the day’s toxic load. A patient with kidney insufficiency will often have a specific gravity between 1.008 to 1.012.
Blood testing: We are able to stage a patient's kidney disease based on creatinine blood level. Creatinine is the most important marker of uremia. It is a by-product of muscle break-down and is always in the bloodstream in small amounts. The kidney removes it continuously and the value stays very steady, unless there is a kidney function problem. Another marker or uremia is BUN, which stands for blood urea nitrogen. This parameter is similar to creatinine but is influenced by dietary protein levels as well as kidney function so it is not as specific to the kidneys as creatinine. These two markers are central to determining the severity of a kidney problem. The higher the values, the more significant the problem. It is also important to monitor blood calcium, phosphorus and electrolyte levels as well as red blood cell concentration as these are all affected by kidney disease.
The balance between calcium and phosphorus in the blood is important. Too much of one or the other will lead to crystals forming in the tissues of the body and weakening of the bones to the extent they may actually become rubbery. The kidney plays an important role in this balance and when kidney function is lost, phosphorus levels begin to rise, making the pet feel ill. Therapy for insufficient kidney function requires monitoring of phosphorus levels and the use of diet and medications to keep phosphorus levels in a reasonable range.
The kidneys play a major role in controlling electrolyte balance as well. In particular, conservation of potassium. Insufficient kidneys lose their ability to conserve potassium and potassium levels begin to drop leading to weakness. Potassium supplements are commonly needed in the treatment of kidney failure if the potassium levels are low.
The kidney also produces a hormone called erythropoietin. This hormone tells the bone marrow to make more red blood cells. In the absence of this hormone, anemia (low red blood cell count) occurs. In some animals it can get so bad that transfusion is necessary. Erythropoietin can be given by injection to alleviate this problem but there are some potential pitfalls in doing this.
Aside from blood and urine testing another important value to monitor is blood pressure. Blood pressure sensors in the kidney help regulate blood pressure in the body. When these are damaged, hypertension (high blood pressure) can result and can damage the kidney further. Blood pressure is commonly measured in kidney failure patients and if it is high, the animal is placed on blood pressure medication to help keep it normal and protect the kidneys from further damage.