Renal function
Blood urea nitrogenBUN
Urea reflects protein metabolism, GI bleeding, and renal perfusion — only partly GFR.
Sample
Serum
Clinical reference range
7 to 20 mg/dL
Adult
Conv: 7–20 mg/dL
Biology
What it measures
Generated in the liver from amino-acid deamination; reabsorbed in the proximal tubule. Reabsorption rises in low flow states.
Clinical use
Why we order it
Volume status (high BUN/Cr ratio in pre-renal AKI), GI bleed (urea load), liver failure (low BUN with low urea synthesis).
Differential
Causes of abnormal values
Causes of HIGH
- ↑Dehydration / pre-renal AKI (BUN/Cr >20)
- ↑GI bleed
- ↑Steroids
- ↑High-protein diet
- ↑Catabolism (sepsis, trauma)
Causes of LOW
- ↓Liver failure
- ↓Low protein intake
- ↓Pregnancy
- ↓SIADH
Related