What is BUN (Blood Urea Nitrogen)?
A substance produced by the liver from the breakdown of protein and eliminated by the kidneys; measured together with creatinine to evaluate kidney function.
BUN (blood urea nitrogen) is formed in the liver as a byproduct of protein metabolism and, like creatinine, is eliminated from the body by the kidneys. Its blood levels are frequently measured together with creatinine to evaluate kidney function, since both tend to build up when the kidneys are not filtering the blood properly.
BUN, however, is more easily influenced by factors outside the kidneys than creatinine is: a high-protein diet, dehydration, bleeding in the digestive tract, and even prolonged fasting can change its levels, even when the kidneys are functioning normally. That is why veterinarians typically evaluate BUN together with creatinine and other tests — when both are elevated together, suspicion of a kidney problem is more consistent than when only one of them is abnormal.
Very low BUN levels can also be relevant and sometimes indicate severe liver disease, since the liver is the organ responsible for producing it. As with any laboratory test, BUN values should always be interpreted by a veterinarian within the pet's overall clinical picture, not in isolation.
Important notice
This calculator is for educational purposes and does not replace a veterinary evaluation. When in doubt, consult a veterinarian.Related terms
Creatinine
A waste product removed by the kidneys, measured in blood to evaluate kidney function; elevated levels usually indicate that the kidneys are not filtering properly.
Chronic Kidney Disease (CKD)
A progressive, irreversible loss of kidney function, very common in senior dogs and cats, that requires ongoing management to control symptoms and slow its progression.
Complete Blood Count (CBC)
A blood test that evaluates red blood cells, white blood cells, and platelets, used to investigate anemia, infection, inflammation, and clotting problems.