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 only one measure of kidney function.
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 working well — but dehydration, a high-protein intake and other conditions move it too, which is why a BUN test is only one measure of kidney function.
The biomarker
- Name: Blood Urea Nitrogen (BUN)
- Units: mg/dL
- Standard range: 6–20 mg/dL (ranges vary by lab).
How to read your result
| Pattern | What it can mean |
|---|---|
| Raised | May reflect kidney disease, dehydration, heart failure, a recent heart attack, gastrointestinal bleeding, a high protein intake, shock, or urinary tract obstruction. |
| Low | May be due to liver disease or failure, a low-protein diet, malnutrition, or overhydration. |
| One measure | A BUN test is only one measurement of kidney function; if kidney disease is suspected, other tests may be needed. |
| eGFR | Providers use blood creatinine to estimate GFR (eGFR); eGFR and urine albumin are the two key markers NIDDK names for chronic kidney disease. |
What moves the needle
- Always read with creatinine, eGFR and urine albumin (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. Dehydration can raise BUN.
- Follow the fasting instruction given. BUN is usually drawn as part of a metabolic panel.
- Test as your clinician directs, usually as part of routine bloodwork.
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.
- It adds information about kidney function, read alongside creatinine, eGFR and urine albumin.
Sources
- MedlinePlus — BUN (Blood Urea Nitrogen) Test
- MedlinePlus — BUN Blood Test
- NIDDK — Tests for Chronic Kidney Disease
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.
