BUN

Measured in mg/dL

A waste product your kidneys clear, which also moves with hydration and how much protein you eat — so it's a rough kidney signal, not a precise one.

What it is

BUN (blood urea nitrogen) measures urea, a waste product your liver makes when it breaks down protein and your kidneys filter out. It's used as a general kidney and hydration signal, and it's usually read alongside creatinine — the BUN-to-creatinine ratio can give clinicians extra context. The honest limitation is that BUN isn't kidney-specific: it can rise with dehydration, a high-protein diet, or certain medications, and can read low with low protein intake or liver issues, so it's interpreted with creatinine and eGFR rather than alone.

Typical range

Adults7–20 mg/dL

Source · ARUP sample report (test 0020023) (2016)

Reference ranges vary between laboratories, and what is normal for you depends on your own history. Your own lab’s range is the one printed on your report.

Worth asking your clinician

Could my hydration or how much protein I eat be influencing my BUN result?
How does my BUN look relative to my creatinine, and does that ratio tell you anything?
Is this a number you'd like to track over time alongside my other kidney markers?