BUN — Normal Range & Interpretation
Full name: Blood Urea Nitrogen
Blood urea nitrogen measures the nitrogen portion of urea, the waste product formed when the liver breaks down protein. The kidneys filter urea and excrete it in urine, so BUN reflects both renal function and protein metabolism. Nurse practitioners pair BUN with creatinine to distinguish prerenal from intrinsic renal causes of kidney dysfunction and to assess hydration status in acute care and primary care settings.
| Male | Female | Unit | Category |
|---|---|---|---|
| 7–20 | 7–20 | mg/dL | BMP (Basic Metabolic Panel) |
Clinical Context
Blood urea nitrogen measures the nitrogen portion of urea, the waste product formed when the liver breaks down protein. The kidneys filter urea and excrete it in urine, so BUN reflects both renal function and protein metabolism. Nurse practitioners pair BUN with creatinine to distinguish prerenal from intrinsic renal causes of kidney dysfunction and to assess hydration status in acute care and primary care settings.
Elevations point to dehydration, acute kidney injury, chronic kidney disease, gastrointestinal bleeding, high-protein diets, catabolic states, and medications such as aminoglycosides, NSAIDs, and ACE inhibitors. Depressed values signal malnutrition, low protein intake, advanced liver disease, pregnancy, and overhydration. A BUN-to-creatinine ratio above 20:1 indicates prerenal azotemia from volume depletion or GI bleed, while a ratio near 10:1 to 15:1 suggests intrinsic renal disease.
Board-style questions on BUN pair interpretation within clinical vignettes rather than recall of the isolated number. Expect questions linking an elevated BUN with dehydration in an older adult on diuretics, prerenal azotemia after GI bleeding, or worsening renal function in a patient started on lisinopril. The exam also tests recognition of the BUN-to-creatinine ratio and the impact of protein intake and hepatic function on baseline values.
Practice Questions
A 72-year-old female presents with three days of vomiting and poor oral intake. Her BMP shows BUN 38 mg/dL with a creatinine of 1.0 mg/dL. Which interpretation is most accurate?
Related Labs
Sources
See also
- Acetaminophen(Drug)
- Ibuprofen(Drug)
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