BUN Test
Also known as: Blood Urea Nitrogen, Urea Nitrogen
What is BUN?
BUN (Blood Urea Nitrogen) measures the amount of nitrogen in your blood from urea, a waste product created when protein is broken down. It is filtered by the kidneys.[MedlinePlus (NIH)]
What This Test Measures
This test measures the concentration of urea nitrogen in the blood. Healthy kidneys remove urea, so high levels may indicate kidney problems.[Mayo Clinic]
Why It's Important
BUN helps assess kidney function and can indicate dehydration, high-protein diet, or kidney disease.[MedlinePlus (NIH)]
BUN is often evaluated alongside creatinine using the BUN/creatinine ratio for better kidney assessment.[Cleveland Clinic]
Who Should Get This Test?
BUN is commonly ordered to assess kidney function and hydration.
Risk Factors
- Routine health screening (part of BMP or CMP)
- Diabetes (monitor kidney function)
- High blood pressure
- Heart disease or heart failure
- Suspected dehydration
- Urinary symptoms or kidney disease symptoms
- Taking medications that affect kidneys (NSAIDs, ACE inhibitors)
- Before and during certain medical treatments
- GI bleeding evaluation (elevated BUN with normal creatinine)
- Monitoring dialysis patients
Screening Schedule
Often included in routine annual bloodwork. More frequent monitoring for diabetes, hypertension, or kidney disease.
What Happens During the Test
A blood sample is drawn from a vein in your arm. BUN is typically part of a basic or comprehensive metabolic panel.
Duration
5 minutes for the blood draw; results usually available within 24 hours
Discomfort Level
Minimal - brief pinch from needle insertion
Risks & Side Effects
BUN testing through blood draw carries very few risks.
- •Minor pain or bruising at the needle site
- •Slight bleeding
- •Rarely, lightheadedness
- •Very rare risk of infection
Normal Range
7 to 20 mg/dL for adults.
Note: Levels may be higher in older adults and those with high-protein diets.
Source: MedlinePlus (NIH)Unit Conversion
Convert between mg/dL and mmol/L
| mg/dL | mmol/L |
|---|---|
| 7 | 2.5 |
| 10 | 3.6 |
| 15 | 5.4 |
| 20 | 7.1 |
| 30 | 10.7 |
| 50 | 17.9 |
High Values
High BUN can indicate kidney disease, dehydration, heart failure, GI bleeding, high-protein diet, or urinary tract obstruction.[Mayo Clinic]
Low Values
Low BUN may indicate liver disease, malnutrition, overhydration, or a very low-protein diet.[Cleveland Clinic]
Test Limitations & Accuracy
BUN is affected by many factors beyond kidney function.
- ⚠High-protein diet increases BUN without kidney disease
- ⚠Dehydration elevates BUN
- ⚠GI bleeding raises BUN (blood is digested as protein)
- ⚠Liver disease lowers BUN (less urea production)
- ⚠Muscle mass affects BUN (more protein metabolism)
- ⚠Heart failure and shock can elevate BUN
- ⚠Certain medications affect levels
- ⚠Less specific for kidney function than creatinine or eGFR
Alternative & Complementary Tests
BUN is typically interpreted alongside other kidney markers.
More specific for kidney function
Best overall measure of kidney function
Calculated to identify cause of elevation
Alternative to creatinine for eGFR calculation
To detect protein or blood in urine
To detect early kidney damage
Frequently Asked Questions
What is the BUN/Creatinine ratio?
The BUN/Creatinine ratio helps identify the cause of kidney problems. A normal ratio is 10:1 to 20:1. High ratios may indicate dehydration or GI bleeding; low ratios may indicate liver disease or malnutrition.
Source: Cleveland ClinicReferences
Related Condition Guides
Medical Disclaimer
This information is for educational purposes only and is not intended as medical advice. Always consult with a qualified healthcare provider for interpretation of test results and medical decisions.
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