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BUN (Blood Urea Nitrogen) Test

⚠️ Update approaching🔬 Evidence: ModerateInternal Medicine
Diğer adları: Blood urea nitrogen, BUN, Urea nitrogen
⚠️

Discuss your test results with your doctor. This page is for informational purposes only and does not provide a diagnosis.

⚡ Key Facts

• An end product of protein metabolism, produced by the liver and excreted by the kidneys • More influenced by non-renal factors than creatinine • BUN/creatinine ratio provides additional diagnostic information • Used alongside creatinine and eGFR for kidney assessment

🧪 What Does This Test Measure?

The BUN test measures blood urea nitrogen, an end product of protein metabolism produced by the liver and excreted by the kidneys.

📋 Why Is It Ordered?

Ordered alongside creatinine for kidney function assessment, dehydration evaluation, BUN/creatinine ratio calculation, and GI bleeding investigation.

🔧 Preparation

The BUN test generally requires no special preparation. However, high-protein meals can significantly elevate urea levels.

📊 Reference Ranges

Commonly used reference ranges: BUN: 7–20 mg/dL (2.5–7.1 mmol/L) BUN/Creatinine ratio: approximately 10–20:1 ⚠️ Reference ranges may vary by laboratory.

⬆️ High Values

Elevated BUN may be associated with decreased kidney function, dehydration, high protein intake, GI bleeding, heart failure, catabolic states, or certain medications.

⬇️ Low Values

Low BUN generally does not cause serious clinical concern. It may be associated with low protein intake, severe liver disease, pregnancy, or overhydration.

⚙️ What Can Affect Results?

Protein intake, hydration status, liver function, GI bleeding, catabolic state, age, and certain medications may affect BUN levels.

🔬 Evidence Summary

Moderate evidence: 1 guideline, 2 landmark observational studies.

📚 Most Important Studies on This Topic

1

KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease

Guideline· Kidney International · 2024 · PMID: 38490803

2

New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race

Observational· New England Journal of Medicine · 2021 · PMID: 34554658

3

A New Equation to Estimate Glomerular Filtration Rate

Observational· Annals of Internal Medicine · 2009 · PMID: 19414839

✅ Key Takeaways

💡

What you learned: BUN is influenced by both kidney function and non-renal factors like protein intake and hydration. It is most informative when evaluated alongside creatinine and eGFR.

⛔

A BUN result alone cannot diagnose kidney disease. Creatinine, eGFR, and clinical context are needed.

🔬 Sources Used on This Page

3 sources · Most recent publication: 2024
📋
Guideline
Expert society and guideline recommendations
1
source
👁
Observational
Observational and cohort studies
2
sources
Overall assessment: Evidence level for this topic is moderate. This page is supported by 1 guideline, 2 observational studies.

📝 Questions to Ask Your Doctor

Be prepared for your appointment. Add questions to your list.

📋 References

[PMID: 38490803] KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney International, 2024.
[PMID: 34554658] New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race. New England Journal of Medicine, 2021.
[PMID: 19414839] A New Equation to Estimate Glomerular Filtration Rate. Annals of Internal Medicine, 2009.
Last reviewed: 4/1/2026
Next review: 4/1/2027

🔗 Related Topics

🩺 Chronic kidney disease🧪 Creatinine🧪 eGFR (tahmini glomerüler filtrasyon hızı)🧪 ALT/AST (karaciğer fonksiyon bağlamı)
⚖️ This page does not replace medical advice. Make treatment decisions with your doctor.
Content is based on scientific studies indexed in PubMed and current clinical guidelines.