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Blood Urea Nitrogen (BUN) Test

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of urea nitrogen in your blood. Urea is a waste product made when your body breaks down protein.

Quick summary

["BUN helps assess kidney function and fluid balance in your body."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
74238-7
Short code
HEDIS 2014 BUN
Synonyms
HEDIS 2014 BUN
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
7
Ref high
20
Critical range
— – 100 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84520
SNOMED
2739004
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Your healthcare provider may order a BUN test to check for kidney problems, monitor kidney disease, or evaluate how well your kidneys are removing waste products from your blood. It can also help diagnose conditions like dehydration, heart failure, or liver disease.

How Is the Test Performed?

A blood sample is taken from a vein, usually in your arm. You may feel a small pinch when the needle is inserted, but it usually doesn’t cause discomfort afterward.

What Do the Results Mean?

While specific ranges vary by lab, higher than expected BUN levels may suggest kidney issues, dehydration, or other health problems. Lower levels might indicate overhydration or liver problems. Your results will be discussed with your healthcare provider in the context of your overall health.

What Can Affect My Results?

Several factors can influence BUN levels, including diet (especially protein intake), dehydration or fluid overload, kidney function, heart disease, and certain medications.

Reference range

Adult: 7-20 mg/dLN/A

Specimen: serum

No special preparation required. Stay well hydrated.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

BUN

Frequently asked questions

What causes elevated BUN levels?
Elevated BUN levels can result from conditions like kidney disease, dehydration, heart failure, or high protein intake. Your healthcare provider will consider your symptoms and other test results to determine the cause.
How long does it take to get my BUN test results?
Results from a BUN test are typically available within a few days, depending on your lab’s processing times. Your healthcare provider will contact you once the results are ready.
Can I eat or drink before my BUN test?
You may be advised to fast for 8–12 hours before the test, but always follow your healthcare provider’s specific instructions to ensure accurate results.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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 16, 2026. · Read our editorial policy