Is my BUN (Blood Urea Nitrogen) normal?
Free blood test checker · Standard + longevity-optimal ranges
What is a normal BUN level?
BUN measures the amount of urea nitrogen in your blood, produced when the liver breaks down dietary protein and the kidneys excrete it. Normal is 7-20 mg/dL. Elevated BUN can indicate impaired kidney function, dehydration, high protein diet, GI bleeding, or heart failure. The BUN/creatinine ratio (normally 10:1 to 20:1) helps distinguish pre-renal causes (dehydration, heart failure) from intrinsic kidney disease. BUN above 30 mg/dL warrants medical evaluation.
| Range | Values |
|---|---|
| Standard Reference | 7–20 mg/dL |
| High Risk | > 30 mg/dL |
What causes abnormal BUN levels?
Elevated BUN is caused by dehydration (most common mild elevation), high protein diet, kidney disease (reduced excretion), congestive heart failure (reduced renal perfusion), GI bleeding (blood protein digested and converted to urea), severe burns, fever, corticosteroid use, and catabolic states. Low BUN can indicate liver disease (reduced urea synthesis), malnutrition, or overhydration.
When should you see a doctor?
See your doctor if BUN is above 25 mg/dL persistently (not explained by dehydration), if BUN/creatinine ratio is abnormal, or if you have symptoms like decreased urine output, swelling, fatigue, or nausea. If BUN is above 30 mg/dL, request creatinine, eGFR, and urinalysis for comprehensive kidney evaluation.
BUN and longevity
BUN is an imperfect kidney marker because it is influenced by non-renal factors — protein intake, hydration status, and catabolism all affect levels independently of kidney function. For this reason, cystatin C and eGFR are preferred for true kidney function assessment in longevity medicine. However, trending BUN over time provides valuable information about protein metabolism and hydration habits. The BUN/creatinine ratio remains a useful clinical tool: a ratio above 20:1 with elevated BUN specifically suggests pre-renal azotemia (dehydration or reduced cardiac output), guiding targeted interventions rather than assuming intrinsic kidney damage.
Where to get a BUN test
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Related biomarkers
These biomarkers are often tested alongside BUN for a more complete picture.
Frequently asked questions
What is a normal BUN level?
What causes high BUN?
What is the BUN/creatinine ratio?
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Sources: Reference ranges based on AHA/ACC, ADA, and AACE clinical guidelines. Biological variation data from Ricos/Westgard database. Longevity-optimal ranges reflect targets used by preventive and functional medicine practitioners.
Last reviewed: April 2026. This tool provides general health information and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your healthcare provider about your specific results.