MLT GlobeUrea / Blood urea nitrogen (BUN)
Kidney Function · also called BUN, Serum urea
What it measures
Urea is the main end-product of protein breakdown, made in the liver and excreted by the kidneys. It is ordered with creatinine to assess kidney function, hydration and protein load.
Specimen and preparation
- Specimen: Serum or lithium-heparin plasma
- Tube: Gold top
- Preparation: Avoid ammonium-heparin tubes. High-protein meals may raise values slightly.
Reference range
| Group | Range |
|---|---|
| Adult (urea) | 15–45 (2.5–7.5) mg/dL (mmol/L) |
| Adult (BUN) | 7–20 mg/dL |
Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.
Causes of high values
- Acute or chronic kidney disease
- Dehydration and reduced kidney perfusion (heart failure, shock)
- Upper gastrointestinal bleeding
- High protein intake or catabolism
- Urinary tract obstruction
- Corticosteroids
Causes of low values
- Severe liver disease
- Low protein diet or malnutrition
- Pregnancy
- Overhydration or SIADH
Method
Enzymatic (urease–glutamate dehydrogenase, kinetic UV)
Good to know
Urea (mg/dL) = BUN × 2.14. A BUN:creatinine ratio above about 20 suggests a pre-renal cause.
Related tests
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