What Is Blood Urea Nitrogen (BUN)?

Blood urea nitrogen (BUN) is a common blood test used to evaluate how well your kidneys are working. It measures the amount of urea nitrogen, a waste product that forms in the liver when your body breaks down protein. This waste is normally filtered out by the kidneys and passed out in urine.

When kidney function slows down, urea builds up in the blood, leading to a higher BUN level. That is why the BUN test is often used to check for signs of kidney damage or dehydration.

The normal range for BUN in healthy adults is usually:

• 7 to 20 mg/dL (milligrams per deciliter)

However, the ideal range can vary slightly depending on your age, overall health, and the lab doing the test.

A high BUN level may suggest:

• Kidney problems
• Dehydration
• High protein intake
• Heart failure
• Certain medications

On the other hand, a low BUN level is less common but may happen with:

• Liver disease
• Malnutrition
• Overhydration

It is important to note that BUN is not a stand-alone test. Doctors usually look at it along with creatinine and other lab results to get a more complete picture of kidney function. The BUN-to-creatinine ratio can also help determine whether a kidney issue is due to damage, dehydration, or another cause.

BUN can be affected by more than just kidney health. For example, if you are dehydrated, your BUN might be temporarily elevated even if your kidneys are healthy. That is why a single test result is not enough for a diagnosis—it needs to be interpreted in the context of your overall health.

Understanding your BUN level gives you and your healthcare provider valuable insight into how your body is processing waste and how well your kidneys are keeping up.

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