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Blood Urea Nitrogen (BUN) Test

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

A blood test that measures urea nitrogen, a protein breakdown waste product used to help assess kidney function, hydration, and nutritional status.

Quick summary

["Your BUN result is most useful when interpreted with kidney function tests such as creatinine and eGFR."]

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

Key facts at a glance

LOINC
54051-8
Short code
HEDIS 2009 MPM-A BUN
Synonyms
HEDIS 2009 MPM-A BUN
Category
kidney
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

What is this test?

The blood urea nitrogen, or BUN, test measures the amount of urea nitrogen in your blood. Urea is a waste product made when the body breaks down protein and is removed from the blood by the kidneys.

Why might I need this test?

BUN is commonly checked to help evaluate kidney function and hydration. It may also be used when monitoring kidney disease, illness, or other conditions that can affect protein metabolism.

How is the test performed?

A clinician or laboratory professional collects a blood sample, usually with a needle placed in a vein. The laboratory measures the BUN concentration, often along with creatinine and estimated glomerular filtration rate, or eGFR.

How do I prepare for the test?

Fasting is usually not required for a BUN test, but follow any instructions provided by your clinician. Drink fluids normally unless you have been given different instructions, and tell the care team about major changes in protein intake, hydration, medications, or supplements.

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

Is a BUN test the same as a urea test?
Yes. The BUN test measures urea nitrogen in the blood, which is closely related to the body's total urea level.
Do I need to fast before a BUN test?
Usually not. If the BUN is part of a larger panel or your clinician has given special preparation instructions, follow those instructions.
Can one BUN result show whether I have kidney disease?
No single result usually establishes a diagnosis. BUN is interpreted with creatinine, eGFR, symptoms, medical history, and sometimes repeat testing.
  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