Know Your Blood Parameter: Blood Urea Nitrogen (BUN)
- Summarised by TGHC Editorial Team
- Jun 23, 2025
- 3 min read
Updated: Dec 29, 2025
Parameter Name
Blood Urea Nitrogen (BUN)
Blood Urea Nitrogen, commonly abbreviated as BUN, is a crucial parameter in the assessment of kidney function and overall metabolic status in the body. It reflects the amount of nitrogen in the blood that comes from urea, a waste product formed in the liver after the body breaks down protein.
Test Type
Blood
This test is performed using a blood sample, typically drawn from a vein in the arm. It is a straightforward procedure that usually requires minimal preparation from the patient, making it a common test in routine health assessments.
Normal Range
7 – 20 mg/dL (adults)
The normal range for BUN levels in adults is generally considered to be between 7 and 20 mg/dL. However, it is essential to note that reference ranges can vary slightly depending on the laboratory and the specific methods used for testing.
High Levels Indicate
Impaired kidney function, dehydration, high protein intake, or GI bleeding.
Elevated BUN levels can be indicative of several underlying issues. For instance, they may suggest that the kidneys are not filtering waste efficiently, a condition often seen in chronic kidney disease or acute kidney injury. Additionally, high levels can arise from dehydration, where the concentration of urea in the blood increases due to reduced fluid volume. A high-protein diet can also elevate BUN levels, as more protein breakdown leads to increased urea production. Furthermore, gastrointestinal bleeding can cause a rise in BUN due to the absorption of blood proteins.
Low Levels Indicate
Malnutrition, liver dysfunction, overhydration.
Conversely, low BUN levels may signify malnutrition, where insufficient protein intake leads to decreased urea production. Liver dysfunction can also play a role, as the liver is responsible for producing urea; any impairment in liver function can reduce BUN levels. Overhydration, where excessive fluid intake dilutes the blood, can also result in lower BUN concentrations.
Why It's Tested
To assess kidney function and detect urea buildup due to reduced filtration.
The primary reason for testing BUN levels is to evaluate kidney function. Since the kidneys play a vital role in filtering waste products from the blood, monitoring BUN can help identify potential issues with renal function. Additionally, it can be instrumental in detecting urea buildup, which may occur when the kidneys are unable to filter waste effectively.
Associated Symptoms (if abnormal)
Fatigue, confusion, nausea, swelling (in kidney failure).
When BUN levels are abnormal, patients may experience a range of symptoms. Common signs associated with elevated BUN levels include fatigue and confusion, which can result from the accumulation of toxins in the blood. Nausea and swelling, particularly in the legs and abdomen, may also occur, especially in cases of kidney failure where fluid balance is disrupted.
What To Do If Abnormal
Re-evaluate hydration status, protein intake; consider creatinine and eGFR tests.
If BUN levels are found to be abnormal, it is crucial to take appropriate steps to address the underlying causes. This may involve re-evaluating the individual's hydration status, adjusting protein intake, or further testing. Additional tests, such as creatinine levels and estimated Glomerular Filtration Rate (eGFR), may be recommended to provide a more comprehensive assessment of kidney health.
Common Conditions Related
Chronic kidney disease, acute kidney injury, liver disease.
Several medical conditions can lead to abnormal BUN levels. Chronic kidney disease (CKD) is a progressive condition where the kidneys gradually lose function over time, often leading to elevated BUN levels. Acute kidney injury (AKI) can also cause a sudden increase in BUN due to a rapid decline in kidney function. Furthermore, liver disease can impact BUN levels, as impaired liver function affects urea production.
Nutrition or Lifestyle Connection
Moderate protein intake, adequate hydration, monitor salt use.
Nutrition and lifestyle choices play a significant role in maintaining healthy BUN levels. A balanced diet that includes moderate protein intake is essential, as excessive protein can elevate BUN levels. Adequate hydration is equally important, as it helps the kidneys function optimally and prevents dehydration. Additionally, monitoring salt intake can contribute to overall kidney health, as high sodium levels can lead to fluid retention and affect kidney function.
References (APA Format)
MedlinePlus. (2023). BUN test.
Mayo Clinic. (2022). Kidney function tests.
Pagana, K. D., & Pagana, T. J. (2021). Mosby’s diagnostic and laboratory test reference.
