We took a hiatus from the discussion of older pets for the past two months to delve into lyme disease and National Pet Week, but now we’ll return to our geriatric series. This month, we will provide information on one of the most common diseases of older pets – chronic kidney failure.
In people, the organ that seems to cause the most problems with age is the heart. In dogs and cats, the kidneys tend to be the organs that fail most frequently. The kidneys have several important functions. When the blood circulates through the kidneys, certain toxins are removed and electrolytes and minerals (sodium, potassium, phosphorus and calcium among others) are selectively removed and replaced as needed to keep them balanced. The kidneys also produce a hormone called erythropoietin that stimulates the production of red blood cells. When the kidneys are compromised, several things can happen. Firstly, since the kidneys filter toxins, those toxin levels gradually increase and eventually make the animals feel sick. Also, the electrolyte and mineral imbalances caused by kidney failure can affect the muscles, bones and nerves. Anemia is also common with kidney failure because of the decreased production of erythropoietin.
Dogs and cats with chronic kidney failure (or chronic renal failure- CRF) will exhibit several signs. Many pets will drink and urinate more because the kidneys lose the ability to concentrate the urine. Their urine is very dilute and will look pale. Vomiting and/or diarrhea are often seen because the toxins that build up can cause ulcers in the stomach and intestines and also cause nausea. That nausea, combined with ulcers that can also occur in the mouth can lead to a decreased appetite. Pets with CRF also will also lose weight and be lethargic because of the toxin build-up, electrolyte imbalances and anemia.
If you see one or several of these signs, especially in an older pet, we will probably want to get samples of blood and urine to evaluate the kidneys. We look at several different values in the bloodwork and urine. In the blood, we measure the BUN and Creatinine- both are toxins that should be excreted by the kidneys but will increase if they are not filtered out. Increases in these values are very significant because it takes a 75% loss of kidney function to see changes in those numbers. So if the BUN and creatinine are elevated, we know that the pet has less than 25% of his kidney function left. We also look at the sodium, potassium, calcium and phosphorus levels in addition to the red blood cell count for anemia. In the urine, we can look at the concentration of the urine, the presence of abnormal amounts of protein and the presence of blood which can indicate secondary urinary tract infection. We can also see if there are any abnormal cells or structures called casts that can indicate certain types of kidney damage.
Our main concern once we diagnose CRF is how to treat it. Unfortunately, we cannot make the kidneys young again. What we can do is to try and support the function they have left as best as possible. One of the things we do is put these pets on a kidney-supportive diet- usually either k/d or NF. These special foods are low in protein (the toxins are by-products of protein use and by lowering protein, that can help to decrease the toxins), balanced in minerals and electrolytes and are very easy to digest. Giving them fluids can also help. If they are very sick, we may hospitalize them for IV fluids initially and then put them on a maintenance program of fluids given under the skin regularly- often daily or every other day. That can be done at the office or we teach owners to do that at home. Some pets also need medications to lower phosphorus levels and raise potassium levels. We also can use anti-nausea and anti-ulcer medications if needed. In pets who are anemic, we can give injections of erythropoietin to increase the red cell count.
As you can see, CRF is a very serious disease, but with the right combination of medications, diet and fluids, we try to improve the quality of life for these pets for as long as possible.