Blood urea / BUN reference ranges
| Test | Normal Range |
|---|---|
| Blood Urea Nitrogen (BUN) | 7–20 mg/dL (2.5–7.1 mmol/L) |
| Blood Urea | 15–43 mg/dL (2.5–7.1 mmol/L as urea) |
| BUN:Creatinine ratio | 10:1 to 20:1 |
What does high BUN mean?
Pre-renal vs renal causes
High BUN with a raised BUN:creatinine ratio (>20:1) suggests a pre-renal cause — dehydration, heart failure, GI bleeding, or high protein intake — where the kidneys are working but receiving less blood flow. High BUN with normal BUN:creatinine ratio (<20:1) suggests intrinsic kidney disease. This distinction helps guide treatment before further tests are done.
Causes of high and low BUN
| Result | Common causes |
|---|---|
| High BUN | Dehydration, kidney disease, high protein diet, GI bleeding, heart failure, corticosteroids |
| Low BUN | Liver disease (reduced urea production), malnutrition, low protein diet, overhydration |
BUN is always interpreted alongside creatinine and eGFR. A single raised BUN without a raised creatinine is often due to dehydration or dietary factors rather than kidney disease.
Questions to ask your doctor
- Is my BUN raised because of dehydration or kidney disease?
- What is my BUN:creatinine ratio?
- Should I drink more fluids and recheck?
Medical Disclaimer: For educational purposes only. Always consult a qualified healthcare professional for diagnosis and treatment.