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Blood Urea Nitrogen

The blood urea nitrogen (BUN) test serves as a fundamental biomarker offering valuable insights into renal function, fluid balance, and overall health status. Understanding the significance of BUN levels is paramount for healthcare practitioners in diagnosing and managing various medical conditions. 

What is Blood Urea Nitrogen?

Blood urea nitrogen (BUN) is a crucial indicator of renal function and nitrogen metabolism, measured through a routine blood test. It represents the concentration of urea, a waste product generated by the liver during protein metabolism, circulating in the bloodstream. 

Normally, urea is filtered out of the blood by the kidneys and excreted in urine, making BUN levels a reflection of both renal filtration capacity and urea production. 

Clinically, BUN serves as a valuable biomarker for assessing kidney function, dehydration status, and protein metabolism.  Elevations in blood urea nitrogen (BUN) levels often indicate impaired renal function, dehydration, gastrointestinal bleeding, or high protein intake.

Understanding the Blood Urea Nitrogen Test

Explanation of Blood Urea Nitrogen Measurement

The blood urea nitrogen (BUN) test measures the amount of nitrogen in the blood that comes from urea, a waste product of protein metabolism.  The BUN test can tell a clinician a lot about a patient’s current health status. 

It assesses the efficiency of kidney function by evaluating how effectively the kidneys are filtering urea from the blood and excreting it in urine.  

BUN is commonly ordered as part of a comprehensive metabolic panel, which reveals liver and kidney function as well as electrolyte status and other important biomarkers.  In addition to being offered as a standalone biomarker in the comprehensive metabolic panel, it is also offered as part of the BUN/creatinine ratio, which provides additional insights into kidney function and hydration status.

Elevations in BUN in the blood mean that the kidneys are not filtering urea nitrogen quickly enough, dehydration, or excessive protein intake.  These elevations may prompt further evaluation and management of underlying conditions such as chronic kidney disease, dehydration, or gastrointestinal bleeding. 

Conversely, low BUN levels can signify liver disease, malnutrition, or overhydration.  

It is important to understand that these test results should be interpreted in the context of the individual’s health history and other diagnostic test results.  

What Causes High BUN Levels?

Renal Dysfunction and Impaired Kidney Function 

High BUN levels often stem from renal dysfunction, where the kidneys cannot effectively filter urea from the bloodstream and excrete it in urine. Conditions such as chronic kidney disease, acute kidney injury, or nephrotic syndrome can impair renal function, leading to elevated BUN levels.

Dehydration and Reduced Renal Perfusion 

Dehydration and reduced renal perfusion can also result in elevated BUN levels as the kidneys conserve water and concentrate urine, leading to increased urea reabsorption and subsequent elevation in BUN concentration. 

Reduced blood flow to the kidneys due to conditions like hypovolemia, heart failure, or shock can contribute to dehydration-induced elevations in BUN.

Gastrointestinal Bleeding and Increased Urea Production

Gastrointestinal bleeding can elevate BUN levels through the increased absorption of blood proteins in the gastrointestinal tract, leading to higher urea production. 

The breakdown of hemoglobin from blood in the intestines results in increased urea formation, contributing to elevated BUN levels in conditions such as upper gastrointestinal bleeding, peptic ulcers, or esophageal varices, highlighting the role of gastrointestinal health in BUN regulation.

High Protein Diet and Urea Formation

Consumption of a high-protein diet can lead to increased urea formation as the body metabolizes excess amino acids. The liver converts amino groups from proteins into ammonia, which is then converted to urea for excretion. 

What Causes Low Blood Urea Nitrogen Levels?

Liver Disease and Malnutrition 

Low blood urea nitrogen (BUN) levels can indicate liver disease and malnutrition. 

In liver dysfunction, reduced BUN levels may result from impaired urea synthesis due to compromised liver function (often seen in severe liver disease or end-stage liver failure), leading to decreased production and excretion of urea. 

Similarly, malnutrition or inadequate protein intake can lead to decreased amino acid metabolism and urea production, contributing to lower BUN levels.

The BUN Blood Test

Sample Requirements and Processing

The BUN test requires a simple blood sample, usually drawn from a vein in the arm using a needle and syringe or via a fingerstick for point-of-care testing. Prior to the test, patients are advised to fast for several hours to ensure accurate results. 

BUN Reference Ranges 

Normal reference ranges for BUN levels typically fall between 6 to 20 mg/dL (milligrams per deciliter), although these values may vary slightly depending on the laboratory and the patient's age, sex, and medical history. 

Reference ranges for children are different: 

Children: 5-18 mg/dL (1.8-6.4 mmol/L)

Again, BUN is typically also used as the BUN/creatinine ratio to assess kidney function, aid in the differentiation of prerenal and intrinsic renal causes of acute kidney injury, and evaluate dehydration status.

Interpretation of BUN Levels

Diagnostic Utility in Assessing Renal Function 

The interpretation of blood urea nitrogen (BUN) levels is integral in assessing renal function, with elevated BUN levels often indicative of impaired kidney function. Higher BUN levels may suggest decreased glomerular filtration rate (GFR) and reduced renal excretion of urea, highlighting the presence of kidney dysfunction. 

Conversely, low BUN levels may indicate enhanced renal clearance and potentially hyperfiltration, although they can also be influenced by factors such as liver disease, malnutrition, or overhydration, emphasizing the importance of considering clinical context in interpreting BUN levels.

Evaluation of Dehydration Status and Fluid Balance 

BUN levels play a crucial role in evaluating dehydration status and fluid balance in patients. During dehydration, reduced renal perfusion leads to increased reabsorption of urea in the kidneys, resulting in elevated BUN levels. Therefore, elevated BUN levels in conjunction with high serum creatinine levels may indicate dehydration, prompting clinicians to initiate appropriate fluid resuscitation strategies. 

Conversely, low BUN levels may suggest overhydration or excessive fluid intake, necessitating further investigation into fluid status and management.

Monitoring Response to Treatment in Kidney Disorders

BUN levels serve as a valuable marker for monitoring the response to treatment in various kidney disorders. In conditions such as acute kidney injury or chronic kidney disease, serial measurement of BUN levels can track changes in renal function over time, guiding the adjustment of therapeutic interventions and assessing treatment efficacy. 

Additionally, in the context of renal replacement therapy, such as hemodialysis or peritoneal dialysis, regular monitoring of BUN levels helps clinicians optimize dialysis parameters and ensure adequate clearance of urea and other waste products. 

Overall, the dynamic nature of BUN levels makes them an essential tool in the ongoing management of kidney disorders.

Natural Support for Elevated BUN Levels

Providing natural support for elevated BUN levels begins by understanding the cause of the elevation, and working with a medical professional to create an individualized plan.  In general, some natural support options to consider include:

Dietary Modifications [3., 4., 5.]

  • Increase consumption of water-rich foods such as fruits and vegetables to promote hydration and support kidney function.
  • Incorporate foods rich in potassium, such as bananas, oranges, and potatoes, to help maintain electrolyte balance and support kidney health.
  • Consider adjusting or decreasing salt intake.
  • Reduce intake of high-protein foods to alleviate strain on the kidneys and lower urea production.

Lifestyle Changes

  • Maintain a healthy weight through regular exercise and physical activity to support overall kidney function.
  • Practice stress-reducing techniques such as yoga, meditation, or deep breathing exercises to promote relaxation and reduce the impact of stress on kidney health.


  • Omega-3 fatty acids: Consider supplementation with fish oil or flaxseed oil to reduce inflammation and support cardiovascular health, which in turn can benefit kidney function.  [2.]
  • Coenzyme Q10 (CoQ10): Known for its antioxidant properties, CoQ10 supplementation may help protect the kidneys from oxidative damage and support overall renal health. [7.]

Natural Support for Low BUN Levels

As with elevated BUN levels, providing support for low BUN levels begins with identifying the cause, and working with a medical professional to create an individualized plan.  Potential natural support options for low BUN include:

Dietary Modifications

  • Increase protein intake through sources such as lean meats, poultry, fish, eggs, dairy products, legumes, and nuts to support urea production and raise BUN levels.
  • Consume foods rich in nitrogen-containing compounds like soybeans, lentils, spinach, and quinoa to provide the necessary building blocks for urea synthesis.

Lifestyle Changes

  • Stay hydrated by drinking an adequate amount of water throughout the day to support kidney function and maintain fluid balance.
  • Engage in regular physical activity to promote metabolic processes and overall health, which can indirectly impact urea production and BUN levels.
Blood Urea Nitrogen (BUN) is a way to measure the amount of nitrogen in your blood that comes from a waste product called urea. Urea is made in your body when protein, which is essential for your cells, gets broken down. This happens in your liver, and then the urea moves through your bloodstream to your kidneys. Your kidneys act like a top-notch waste management system, filtering out urea and other waste products from your blood and turning them into urine. So, BUN essentially gives us an idea of how well your liver and kidneys are working together to keep your body clean from the inside.
If Your Levels Are High
Elevated BUN levels might mean that your body is breaking down protein faster than usual, possibly due to a high-protein diet, intense exercise, or stress. Some medications, like steroids or certain antibiotics, could also cause higher BUN levels. On the other hand, it could suggest that your kidneys aren't effectively removing waste from your blood, which might be due to dehydration or a condition affecting kidney function. Additionally, liver disease and some digestive issues could raise BUN levels, as these problems can impact how your body processes and gets rid of waste products.
Symptoms of High Levels
Symptoms of high levels of BUN could include fatigue, a decrease in appetite, nausea, vomiting, and changes in mental status such as confusion or reduced concentration.
If Your Levels are Low
Low BUN levels might mean that your body isn't breaking down protein as well as it should. This could be because you're not eating enough protein, you're not getting the right nutrients, or there might be a problem with your liver. Some medications, like those used for inflammation or infections, can also cause low BUN levels. Drinking too much water can dilute the urea in your blood, leading to lower BUN levels as well. Conditions like liver disease or damage, or being severely undernourished, could also be behind these results.
Symptoms of Low Levels
Symptoms of low levels of BUN may not be easily noticeable. However, in some cases, individuals might experience fatigue, weight loss, or a decrease in muscle mass.
See References

[1.] Edelstein CL. Chapter Six - Biomarkers in Acute Kidney Injury. ScienceDirect. Published January 1, 2017. ‌

[2.] Lauretani F, Maggio M, Pizzarelli F, Michelassi S, Ruggiero C, Ceda GP, Bandinelli S, Ferrucci L. Omega-3 and renal function in older adults. Curr Pharm Des. 2009;15(36):4149-56. doi: 10.2174/138161209789909719. PMID: 20041816; PMCID: PMC2863302. 

[3.] National Institute of Diabetes and Digestive and Kidney Diseases. Eating Right for Chronic Kidney Disease | NIDDK. National Institute of Diabetes and Digestive and Kidney Diseases. Published 2019. 

[4.] Staff familydoctor org editorial. Chronic Kidney Disease (CKD) | Chronic Kidney Disease and Nutrition. Published December 28, 2016.

[5.] Syauqy A, Hsu CY, Lee HA, Rau HH, Chao JC. Association between Dietary Patterns and Kidney Function Parameters in Adults with Metabolic Syndrome: A Cross-Sectional Study. Nutrients. 2020 Dec 24;13(1):40. doi: 10.3390/nu13010040. PMID: 33374257; PMCID: PMC7823384.

[6.] Tietz NW (Ed): Clinical Guide to Laboratory Tests, 3rd ed. W. B. Saunders, Philadelphia, PA, 1995.

[7.] Zhao, S., Wu, W., Liao, J. et al. Molecular mechanisms underlying the renal protective effects of coenzyme Q10 in acute kidney injury. Cell Mol Biol Lett 27, 57 (2022).

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Blood Urea Nitrogen

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