Feb 15 2009
BUN & Creatinine: Determining kidney function by bloodwork
Kidney problems are a major finding in older pets, and in some younger pets, too, especially since the increase in tick borne illnesses.
There are 2 main readings we look at with bloodwork that tell us about kidney functioning. They are: BUN (blood urea nitrogen) and Creatinine.
Urea should be excreted by the kidneys. In an aged kidney where cells are starting to die or shrivel, the kidney may not excrete all of this urea as it should but some may remain for a short time longer than necessary in the blood stream. Thus, on bloodwork, the blood levels of urea (BUN) can be slightly (and only slightly) increased. Not a big deal. Also, urea is made by the liver (thus low BUN in liver disease) but in an animal who eats a high protein diet (like your dog on his raw diet), more urea than typical is made by the liver, and the kidney, in order to not overwork itself and put undo pressure on itself, will still excrete the same amount or only slightly higher levels of urea at a time, thus BUN can be increased for this reason as well. Especially if your vet does not tell you to fast your dog from eating for 8-12 hours before bloodwork, this number, unless extremely elevated, is not a significant finding alone (unless accompanied by a high creatinine).
Creatinine is a much better stand alone test to evaluate kidney functioning. That is because a high creatinine level points to a kidney issue, and a kidney issue only. Creatinine is excreted by the kidney is a normal healthy kidney and should not be in excess in the blood. If it is, especially as it continues to rise in levels, it will cause internal toxicity and neurological symptoms. The kidneys try to fight this problem by flushing themselves (making a dog very thirsty and urinating extreme amounts) when this occurs. This is often the first symptom noticed: the excessive urination and thirst!
A kidney on ultrasound in an older dog can look slightly smaller, and this is normal. Kidney cells can die off after time, but do know it takes about 75% of kidney cells to diet before kidney failure symptoms are seen. And luckily, dogs can live just fine after treatment even in these cases. When kidney symptoms do appear, of course, a low protein/ low phosphorus diet is highly recommended.
Christine, LVT
