Chronic Renal (Kidney) Failure

The kidneys are made of thousands of tiny filtration units called nephrons. Once a nephron is destroyed by a disease, it cannot regenerate; this means that we all have a finite number of nephrons to last us our whole lives. Fortunately, we have many extra nephrons, so many extra that overall kidney function does not fall behind until we are down to about 1/6 of our original number of nephrons.

Nephrons can be destroyed quickly or slowly. Usually, by the time less than 1/6 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 make 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.

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 (they fail to make concentrated urine). The body produces numerous toxins on a moment by moment basis. These toxins circulate to the kidneys where, dissolved in water, 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 over a long time period, they lose their ability to concentrate urine and more water is required to excrete the same amount of toxin. The animal will begin to drink more and more to provide the failing kidneys with enough water. Ultimately, the animal cannot drink enough and toxin levels begin to rise. Weight loss, listlessness, nausea, constipation, and poor appetite become noticeable. It is common for animals, especially cats, to have a long history of excessive water consumption when they finally come to the vet with one of the latter complaints.