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Bunserplscnc

Published: July 31, 2026Updated: August 15, 2026

A blood test that measures the amount of urea nitrogen in your blood to evaluate how well your kidneys are working.

Quick summary

{"Measures urea nitrogen waste product in your blood","Helps assess kidney function and detect kidney problems","Often part of routine blood work (metabolic panel)","Abnormal levels may indicate dehydration, kidney issues, or other conditions","Simple blood test with minimal risks"}

Medically reviewed by WellAlly Editorial TeamLast reviewed August 15, 2026Editorial policy

Key facts at a glance

LOINC
14937-7
Short code
BUN
Synonyms
BUN SerPl-sCnc
Category
chemistry
Sample
serum
Container
Serum separator tube (SST) or plain red-top tube; plasma (EDTA or heparin) acceptable for some methods
Units
not specified
Ref low
2.5
Ref high
7.1
Critical range
2 not specified – 35.7 not specified
Fasting
false
Population
adult
Sex
all
Age range
≥ 0 years
Method
Enzymatic method (urease) or spectrophotometric method
CPT
84520
SNOMED
273967001
Specimen volume
1.0-2.0 mL serum or plasma minimum
Stability
Room temperature: 24-48 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C): several months
Hemolysis max
50
Lipemia max
300
Icterus max
60
TAT
1–24 hours
Order
routine

What is this test?

The Blood Urea Nitrogen (BUN) test measures the amount of urea nitrogen in your blood. Urea nitrogen is a waste product that forms when your body breaks down protein from food. Normally, your kidneys filter urea nitrogen out of your blood and excrete it in urine. This test helps doctors see how well your kidneys are removing this waste.

Why do I need this test?

Your doctor may order a BUN test as part of a routine health check or if you have symptoms suggesting kidney problems, such as swelling in your legs, changes in urination, or fatigue. It helps monitor existing kidney conditions and evaluate how well your kidneys are functioning.

How do I prepare for the test?

You may need to fast (not eat) for 8-12 hours before the test. Your doctor will tell you if fasting is necessary. Inform your doctor about all medications, vitamins, or supplements you take, as some medicines can affect test results. Drinking water before the test is usually allowed.

What happens during the test?

A healthcare professional will draw a small blood sample from a vein in your arm using a needle. You may feel a brief pinch or sting. The sample is sent to a laboratory for analysis. The test is quick and usually takes only a few minutes.

Understanding your results

BUN levels are measured in millimoles per liter (mmol/L). Normal ranges vary by laboratory but are typically around 2.9-8.2 mmol/L. Higher than normal BUN levels may indicate kidney problems, dehydration, or high protein intake. Lower than normal levels may be due to liver disease or low protein intake. Your doctor will interpret your results based on your overall health and other test findings.

Reference range

2.5-7.1 mmol/Lnot specified

Specimen: serum

No special preparation or fasting required

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Frequently asked questions

Does the BUN test hurt?
You may feel a brief sting or pinch when the needle is inserted to draw blood. This discomfort is usually minimal and goes away quickly. Some people may experience slight bruising at the injection site afterward.
How long does it take to get results?
Results are typically available within 1-2 days, depending on the laboratory. Your doctor's office will contact you with the results or discuss them at your follow-up appointment.
What can affect my BUN levels?
Several factors can influence BUN results, including: high-protein diet, certain medications (such as diuretics or steroids), dehydration, liver disease, heart failure, and kidney problems. It's important to tell your doctor about any medications or health conditions you have.
Is a high BUN level always serious?
Not necessarily. A high BUN level can have many causes, including dehydration (which is common and often treatable) or a high-protein diet. Your doctor will consider your symptoms, medical history, and other test results to determine if further testing is needed.
Do I need to do anything after the test?
After the blood draw, you can resume your normal activities immediately. If you fasted before the test, you may want to eat something afterward. If you experience persistent bleeding, severe pain, or swelling at the injection site, contact your healthcare provider.
  1. 1
    MedlinePlus - Blood Urea Nitrogen (BUN) TestSource
  2. 2
    Mayo Clinic - BUN (Blood Urea Nitrogen) TestSource
  3. 3
    National Kidney Foundation - BUN TestSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 15, 2026. · Read our editorial policy