Blood Urea Nitrogen (BUN)
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Blood urea nitrogen test; evaluates kidney function and protein metabolism.
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🧪 Blood Urea Nitrogen (BUN) Test
Parameter | Details |
|---|---|
Test Name | Blood Urea Nitrogen (BUN) |
Sample Type | Serum (venous blood) |
Fasting Required | ✅ Recommended (8–10 hours) for most accurate results |
Normal Range | 7–20 mg/dL (may vary slightly by lab and age) |
Primary Organ | Kidneys |
🧬 What is BUN?
BUN measures the amount of nitrogen in the blood that comes from urea, a waste product of protein metabolism. Urea is produced in the liver and excreted by the kidneys through urine.
🩺 Why is the BUN Test Done?
Purpose | Details |
|---|---|
🔍 Assess Kidney Function | High BUN indicates that the kidneys may not be excreting waste efficiently |
🧬 Evaluate Liver Function | Low BUN may be seen in severe liver disease (impaired urea production) |
💊 Monitor Treatment | Used in people with chronic kidney disease (CKD), heart failure, or liver disease |
🧪 Pre-Surgical Evaluation | Part of routine kidney function checks |
🚨 Investigate Symptoms | Used when symptoms of uremia or kidney failure (fatigue, swelling, confusion) are present |
📈 Interpreting BUN Levels
BUN Level | Possible Interpretation |
|---|---|
High (>20 mg/dL) | Kidney dysfunction, dehydration, high-protein diet, GI bleeding, heart failure |
Low (<7 mg/dL) | Liver disease, malnutrition, overhydration, low protein intake |
⚠️ Conditions That Raise BUN
- Acute or chronic kidney disease
- Urinary tract obstruction
- Severe dehydration
- Heart failure
- Shock or severe burns
- GI bleeding (digested blood = protein)
🔽 Conditions That Lower BUN
- Severe liver damage (cirrhosis)
- Malnutrition or low-protein diet
- Overhydration (dilutional)
- Pregnancy (increased plasma volume)
🧪 Recommended Tests with BUN
Test | Reason |
|---|---|
Serum Creatinine | To calculate BUN/Creatinine ratio (normal: ~10:1 to 20:1) |
eGFR | Assesses kidney filtration capacity |
Urea (Blood) | May be reported alongside BUN in some regions (like Europe) |
Electrolytes (Na⁺, K⁺) | For full renal function panel |
Urinalysis | To detect protein, blood, casts in urine |
📊 Summary Table
Test Name | Blood Urea Nitrogen (BUN) |
|---|---|
Sample Type | Serum (blood) |
Fasting | Recommended (8–10 hours) |
Normal Range | 7 – 20 mg/dL |
High Indicates | Kidney dysfunction, dehydration, high protein intake |
Low Indicates | Liver disease, malnutrition |
Used In | CKD, liver failure, heart failure, routine health check |
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