Quick Look

The Blood Urea Nitrogen (BUN) test measures the amount of urea nitrogen in your blood to see if your kidneys are working properly. Your age and sex can affect BUN levels. Unusual levels might signal a health issue, such as kidney damage.

Blood Urea Nitrogen (BUN)

Here’s how your body usually forms and eliminates urea nitrogen:

• Your liver produces ammonia, containing nitrogen, by breaking down proteins used by your body’s cells.
• Nitrogen combines with elements like carbon, hydrogen, and oxygen to create urea, a chemical waste product.
• Urea travels from your liver to your kidneys through your bloodstream.
• Healthy kidneys filter urea and remove other waste products from your blood.
• Filtered waste products exit your body through urine.

This test can indicate if your urea nitrogen levels are higher than normal, suggesting potential issues with kidney function.

Why it’s done

You might need a BUN test if:

• Your doctor suspects kidney disease or damage.
• Your kidney function needs evaluation, especially with chronic conditions like diabetes or high blood pressure.
• To assess the effectiveness of dialysis treatment during hemodialysis or peritoneal dialysis.
• As part of a blood test group to diagnose various conditions like liver damage, urinary tract obstruction, congestive heart failure, or gastrointestinal bleeding. However, an abnormal BUN result alone doesn’t confirm these conditions.
• If kidney concerns are primary, your blood test for urea nitrogen levels may also include measuring creatinine levels. Creatinine, another waste product, is filtered out by healthy kidneys, and high blood levels may indicate kidney damage.
• Your doctor might assess your kidneys’ waste removal efficiency by calculating your estimated glomerular filtration rate (GFR) through a blood sample. GFR estimates the percentage of kidney function.

Results

The normal blood urea nitrogen levels vary based on age and sex:

• Children aged 1 to 17 years: Between 7 and 20 mg/dL.
• Adult women and individuals assigned female at birth: Between 6 and 21 mg/dL.
• Adult men and individuals assigned male at birth: Between 8 and 24 mg/dL.

High BUN

High BUN levels may suggest that your kidneys aren’t working as they should. However, even if your kidneys are working properly, you may have elevated BUN levels from the following:

• High-protein diet.
• Dehydration.
• Aging (infants and children have lower BUN levels).
• Certain medications, including carbamazepine, methotrexate and tetracycline.
• Burns.
• Blockage in your urinary system that prevents you from peeing.
• Stress.
• Heart attack.
• Gastrointestinal (GI) bleeding.

Low BUN

Low levels are uncommon, but they may be attributed to:

• Low-protein diet: A diet lacking in sufficient protein.
• Small body type: Individuals with a smaller body size may have lower BUN levels.
• Overhydration: Excessive water intake leads to diluted BUN levels.
• Liver disease: Impaired liver function can impact BUN levels.

Summary

Urea nitrogen, a waste product created in the liver during protein breakdown, can lead to health issues if its levels are too high or too low in your blood. If you experience symptoms indicating abnormal urea nitrogen levels, it’s important to consult with a healthcare provider. They may recommend a blood urea nitrogen (BUN) test to assess your kidney function and determine appropriate treatment.

References:

1. (N.d.). Retrieved from https://www.mayocliniclabs.com/test-catalog/overview/81793 
2. professional, C. C. medical. (n.d.). Retrieved from https://my.clevelandclinic.org/health/diagnostics/17684-blood-urea-nitrogen-bun-test