BUN — Protein Waste and Kidney Clearance
Blood urea nitrogen tracks protein waste the kidneys clear — but dehydration and diet move it too, so it is never read alone.
Blood urea nitrogen measures the waste that forms as your body breaks down protein and that your kidneys remove in urine. Higher-than-normal BUN may signal the kidneys are not clearing well — but dehydration and a high-protein diet move it too, which is why it is never read alone.
The biomarker
- Name: Blood Urea Nitrogen (BUN)
- Units: mg/dL
- Standard range: 6–20 mg/dL (varies between laboratories).
- Optimal range: no separate "optimal" band is published; the BUN-to-creatinine ratio carries more information than BUN by itself.
How to read your result
| Pattern | What it can mean |
|---|---|
| Raised | May reflect reduced kidney clearance, dehydration, a high-protein intake, gastrointestinal bleeding, or heart failure. |
| Raised with normal creatinine | More often points to dehydration or diet than to the kidney. |
| Low | Can occur with liver disease, very low protein intake, or overhydration — usually less clinically loaded than a raised value. |
| With creatinine | BUN and creatinine are interpreted together, never BUN alone. |
| eGFR | eGFR, calculated from creatinine, is the better single measure of kidney function. |
| Timing | A single raised value after a hot day or a heavy protein meal is weak evidence of anything. |
What moves the needle
- Always read with creatinine, eGFR and urine ACR before drawing any conclusion about kidney function.
- Do not cut protein on a BUN reading alone. That decision belongs to a clinician.
- Arrive normally hydrated. A dehydrated draw inflates the number.
- Follow the fasting instruction given. BUN is usually drawn as part of a metabolic panel.
- Test annually with routine bloodwork, or as directed.
Why this test is worth asking for
- It appears on the standard comprehensive metabolic panel, so there is rarely a reason to order it separately.
- Paired with creatinine, it separates a dehydration or diet effect from a genuine kidney-clearance question.
- A trend across repeated panels is more informative than a single value drawn once.
Sources
AgeGen lab guides are educational only. We do not provide medical diagnosis, prescribe brands, or recommend specific doses. Talk to a licensed clinician before changing your supplement or medication routine.
