Kidney Health

Blood urea nitrogen (BUN)

Optimal Result: 6 - 24 mg/dL, or 2.14 - 8.57 mmol/L.

Urea nitrogen is a waste product formed during the process in which our bodies break down proteins. After a protein is deconstructed, the liver produces nitrogen-containing ammonia. The nitrogen reacts with other elements in our bodies (such as carbon, hydrogen, and oxygen) to form urea. Urea then travels through the liver and into the kidneys via the bloodstream. Healthy kidneys should filter out urea and other chemical waste products from the blood through urine.

- A blood urea nitrogen (BUN) test measures the amount of nitrogen in our blood that has been created by urea and is typically ordered to assess kidney function.

- An unusually high BUN level may indicate that the kidneys are unable to effectively remove urea from the blood. As such, BUN tests can also be used to track the progress of a kidney disease.

- Additionally, a BUN test may be run to assess the functionality of the kidneys prior to certain surgeries or procedures that require the use of drugs that can damage the kidneys.

- Further, BUN tests are often run in tandem with creatinine or renal panels to help identify kidney dysfunction.

Symptoms of kidney dysfunction include:

- Fatigue, lack of concentration, poor appetite, or trouble sleeping

- Edema (swelling or puffiness) around the eyes, face, wrists, abdomen, or ankles

- Decrease, discoloration, or burning of urine

- Mid-back pain

- High blood pressure

It is worth noting that in a normal, health pregnancy BUN concentrations will fluctuate. 

Normal Ranges in mg/dL by ages:

0-2 years:      4-15  
3-16 years:   
9-18  
17-64 years:  8-22
>64 years:    10-28 

What does it mean if your Blood urea nitrogen (BUN) result is too low?

Low BUN levels are not common and are not a cause for concern. Occasionally, severe liver disease, malnutrition, or over-hydration can cause BUN levels to be unusually low; however, the BUN test is not typically used to diagnose or monitor these conditions. 

What does it mean if your Blood urea nitrogen (BUN) result is too high?

Increased BUN levels suggest kidney impairment

Impairment can be acute, chronic, damage, or failure.

It may also be due to a condition that has decreased blood flow to the kidneys, such as:

- congestive heart failure,

- recent heart attack,

- shock,

- stress,

- severe burns,

- or dehydration.

Excessive protein breakdown will also elevate BUN levels, which can result from a high protein diet or gastrointestinal bleeding

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