Urea (BUN) – Blood Urea Nitrogen

The Blood Urea Nitrogen (BUN) test measures the amount of nitrogen in the blood that comes from urea, a waste product formed by the liver when it breaks down protein. BUN is filtered out of the blood by the kidneys and excreted in urine. This test is commonly used to evaluate kidney function and hydration status.

1. What Is BUN?

• BUN stands for Blood Urea Nitrogen, which reflects the amount of urea nitrogen in the blood.

• Urea is produced in the liver as a byproduct of protein metabolism and is excreted by the kidneys.

• BUN levels are influenced by kidney function, liver function, and hydration status.

2. Why Is the BUN Test Performed?

This test is used to:

• Evaluate kidney function and detect kidney disease.

• Assess hydration status and blood volume (e.g., in dehydration or heart failure).

• Monitor individuals with chronic kidney disease (CKD) or on dialysis.

• Check for complications from medications that affect the kidneys.

3. BUN Reference Range

• Normal range: 7 – 20 mg/dL (may vary slightly by lab)

• Levels may vary based on age, gender, protein intake, and muscle mass.

4. Interpreting BUN Results

🔹 High BUN:

• May indicate kidney dysfunction, dehydration, heart failure, high protein diet, or gastrointestinal bleeding.

• Temporary increases may also occur with stress, trauma, or corticosteroid use.

🔹 Low BUN:

• May be caused by liver disease, malnutrition, or overhydration.

• Low BUN is less common and typically less clinically significant than high BUN.

5. What Can Affect BUN Levels?

• Kidney and liver function

• Hydration status (dehydration increases BUN; overhydration decreases it)

• Dietary protein intake and catabolism

• Medications such as diuretics, antibiotics, or chemotherapy drugs

6. How Is the Test Performed?

• A blood sample is drawn from a vein.

• Fasting is not typically required unless part of a larger metabolic panel.

7. When to See a Doctor

🚨 Consult your healthcare provider if you:

• Have symptoms of kidney disease (e.g., swelling, fatigue, changes in urination).

• Are on medications that may affect kidney function.

• Receive abnormal BUN results requiring further evaluation or follow-up.

🔹 Key Takeaways

✅ BUN is a key indicator of kidney health and hydration status.

✅ Elevated levels may indicate kidney dysfunction, dehydration, or protein metabolism issues.

✅ Often used with creatinine for a more complete picture of kidney function.