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Dear Daisy Dog

My dog's kidney function is impaired, and my vet wants to check his blood periodically to measure his kidney values. Can you help me understand these tests?

Daisy Responds

Your veterinarian wants to monitor a number of values, including BUN, creatinine and phosphorus.

Using the results of these blood tests and a urinalysis, as well as information on your dog’s energy and appetite, your veterinarian will be able to regulate his diet and medications to keep him happy and energetic for as long as possible.

BUN (blood urea nitrogen) is made by the liver from ammonia, a breakdown product of dietary proteins. It is excreted by the kidneys, so excess BUN in the blood may indicate decreased kidney function. Non-kidney problems can also increase BUN.

Creatinine, formed during energy production by the skeletal muscles, is also excreted by the kidneys. Increases in BUN and creatinine occur when 75% of kidney function has been lost.

Phosphorus is also excreted by the kidneys, so increased phosphorus in the blood is another indication of kidney dysfunction. Phosphorus can be increased for other reasons as well, but if BUN, creatinine and phosphorus are elevated, it's likely that 85% of kidney function has been lost.

Other lab changes associated with kidney dysfunction include electrolyte changes and decreased excretion of pancreatic enzymes.

Eventually the dog with kidney failure develops anemia (low red blood cell count) because the failing kidneys secrete less-than-normal amounts of erythropoietin, a hormone which stimulates red blood cell production.

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