Guides Β· Published 2026-07-17
What Is BUN? Reading the Kidney Marker on a Pet Lab Report
Plenty of people arrive here after seeing three letters β BUN β on a lab report and wondering what they mean. BUN often appears right next to creatinine when looking at kidney status, but because it also responds to factors outside the kidneys, it's hard to read on its own. This guide covers what BUN reflects, when it can move up or down, and how a good log helps when you talk it over with your vet.
What BUN is
BUN is short for blood urea nitrogen. It's a value that looks at how much urea β a waste product formed as the body breaks down protein β remains in the blood.
Most of that urea leaves through the kidneys and out in the urine, so the amount left in the blood indirectly reflects the kidneys' clearing work. At the same time, it also responds to other factors like the body's hydration and diet.
Why it's read as a kidney marker
Because the kidneys handle clearing this waste, slower excretion can leave a bit more urea in the blood and nudge BUN upward. That's why it's often referenced when looking at kidney status.
That said, BUN is less a kidney-only marker and more a value where several signals overlap. So it's usually placed beside other markers like creatinine (CREA) and SDMA and read within their relationship to one another.
What to look at when it reads high
A BUN value above the reference range brings kidney clearance to mind, but factors outside the kidneys can lift the number too. Below is context a vet weighs when reading BUN.
- Dehydration or changes in water intake
- A high-protein diet or a recent meal before the test
- Digestive factors such as GI bleeding
- The trend of its ratio to creatinine (BUN/CRE)
When it reads low or unclear
BUN can also read low. A low-protein diet, being well hydrated, and factors tied to how the liver forms urea can all push the value downward.
A low value doesn't settle anything on its own. Here too, it's more balanced to read it alongside other markers and your pet's condition, within the trend rather than in isolation.
Good things to know around test day
BUN responds fairly readily to diet and hydration, so what your pet ate before the test and whether they were dehydrated can shape the value. Noting the circumstances of the test day makes the number much easier to revisit later.
The exact reference-range numbers differ from lab to lab and machine to machine, so read against the range printed on that lab's report. Comparing where a value sits within its own range is safer than comparing raw numbers across sources.
Why logging matters
Because BUN is easily swayed by moment-to-moment conditions like diet and hydration, a run of readings tells a more reliable story than any single number. When results are scattered, that trend is easy to miss.
Gathering results in one place and tracking the trend alongside creatinine makes it easier to discuss today's value in a wider context with your vet. When and how things shifted becomes a strong starting point for the conversation.
Pawsitive does not replace veterinary diagnosis, prescription, or treatment. AI analysis results are for reference only. Please consult a veterinarian if your pet shows any health concerns.