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Complete Guide to Blood Urea Nitrogen (BUN) Lab Values: Nursing Lab Values

Written by Jon Haws, BS, BSN, RN, Alumnus CCRN | 6-Jun

Introduction To Blood Urea Nitrogen (BUN) Nursing Lab Value

Blood Urea Nitrogen (BUN) lab values play a significant role in assessing kidney function and overall health. As a crucial component of routine blood tests, BUN levels provide valuable insights into the body's waste elimination process and the functioning of the kidneys. 

In this blog post, we will explore the significance of BUN lab values, what they indicate about kidney health, and how a nurse utilizes this information to diagnose and monitor various conditions. 

Before we go any further I want to offer you a free copy of our "63 Must Know Lab Values for Nurses" book (just pay shipping) . . . click below to grab your copy!

Blood Urea Nitrogen (BUN) Nursing Points

  • Normal Lab Value Range For Blood Urea Nitrogen (BUN)
    • 7-20 mg/dL
  • Pathophysiology of Blood Urea Nitrogen (BUN)
    • Protein is broken into amino acids -> Ammonia
    • Ammonia converted to urea
    • Urea excreted via kidneys
  • Special Considerations for Blood Urea Nitrogen (BUN)
    • Collect blood samples in a green top tube
    • Submitted in multiple panels
      • Chem 7/Chem 10
      • CMP
      • Renal panel

What Does Blood Urea Nitrogen (BUN) Mean in a Blood Test?

BUN stands for Blood Urea Nitrogen, and it is a measurement obtained from a blood test that assesses kidney function and overall health. BUN levels reflect the amount of nitrogen in the blood that comes from urea, a waste product produced when the body breaks down protein.

As we eat food, we take in different types of protein via the GI tract.  That protein is broken down into amino acids. During this process, the amino acids are broken down further and we're left with ammonia.

This ammonia is then transported to the liver, and it's converted to a waste product known as urea. That urea is then kicked out of the kidneys and excreted in urine.

So what happens if the kidneys aren't working? Well, that means that urea is not going to be excreted, and it's going to build up in the blood. That's going to be detectable with the blood urea nitrogen, or the BUN test.


What Causes Blood Urea Nitrogen (BUN) Lab Value Levels to be High or Low?

Blood Urea Nitrogen (BUN) levels can be influenced by various factors, leading to either high or low values. Here are some common causes:

Elevated BUN Lab Value Levels

This may indicate kidney dysfunction or impairment, as the kidneys are responsible for filtering and excreting urea from the body.

  • Dehydration
  • Kidney disease
  • Heart failure
  • Urinary tract obstruction
  • Gastrointestinal Bleeding
  • Urinary Tract Infection (UTI)
  • Certain medications

Diseases Caused by High Blood Urea Nitrogen (BUN) Lab Values

 

  • Kidney Disease: Chronic kidney disease (CKD) or acute kidney injury (AKI) can lead to elevated BUN levels. When the kidneys are not functioning properly, they struggle to effectively filter and excrete urea, resulting in its accumulation in the bloodstream.
  • Dehydration: Insufficient fluid intake or excessive fluid loss, such as through vomiting, diarrhea, or excessive sweating, can lead to dehydration. Dehydration concentrates the blood, increasing BUN levels.
  • Urinary Tract Obstruction: Blockages in the urinary tract, such as kidney stones, tumors, or an enlarged prostate, can impede urine flow and lead to elevated BUN levels.
  • Heart Failure: In congestive heart failure, the heart's pumping capacity is compromised, causing reduced blood flow to the kidneys. This can result in impaired kidney function and increased BUN levels.
  • Gastrointestinal Bleeding: Conditions like stomach ulcers, gastrointestinal tumors, or gastrointestinal bleeding can cause blood loss. The breakdown of blood cells releases hemoglobin, which is converted to urea, leading to elevated BUN levels.
  • Urinary Tract Infection (UTI): Severe urinary tract infections that involve the kidneys, known as pyelonephritis, can impair renal function and cause a rise in BUN levels.
  • Certain Medications: Some medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs), certain antibiotics, and diuretics, can affect kidney function and result in elevated BUN levels as a side effect.

How Do You Fix High Lab Value Levels of Blood Urea Nitrogen (BUN)?

Treating high Blood Urea Nitrogen (BUN) levels involves addressing the underlying cause. The specific approach will depend on the condition or factors contributing to the elevated BUN. Here are some general strategies that the nurse may do:

  • Hydration: If dehydration is causing high BUN levels, the primary focus is to restore fluid balance. Increasing fluid intake, either orally or intravenously, helps to dilute the blood and improve kidney function.
  • Addressing Kidney Disease: For individuals with chronic kidney disease (CKD), managing the underlying condition is crucial. This may involve medication, dietary changes (such as reducing protein intake), blood pressure control, and regular monitoring of kidney function.
  • Treating Urinary Tract Obstruction: If a urinary tract obstruction is the cause, the blockage needs to be identified and treated. This may involve procedures like removing kidney stones or addressing the underlying cause of the obstruction.
  • Managing Heart Failure: In cases where heart failure contributes to elevated BUN levels, treatment aims to improve heart function and reduce fluid retention. Medications, lifestyle modifications, and possibly device implantation or surgical interventions may be necessary.
  • Treating Infections or Inflammation: If a urinary tract infection or other infection/inflammation is present, appropriate antimicrobial or anti-inflammatory therapy may be prescribed to resolve the underlying issue.
  • Adjusting Medications: In some cases, medications that contribute to high BUN levels may need to be adjusted or discontinued. This should only be done under the guidance of a healthcare professional.

Decreased BUN Lab Value Levels

Decreased Blood Urea Nitrogen (BUN) levels can be influenced by various factors. Here are some common causes:

  • Liver Disease
  • Malnutrition
  • Overhydration
  • Pregnancy
  • Severe Liver Damage

Diseases Caused by Low Blood Urea Nitrogen (BUN)

  • Liver Disease: Severe liver diseases, such as cirrhosis or hepatitis, can lead to reduced BUN levels. The liver is responsible for the production of urea, so when liver function is compromised, there may be a decrease in urea production and subsequent lower BUN levels.
  • Malnutrition: Inadequate protein intake or malnutrition can result in decreased urea production, leading to lower BUN levels. This can occur in individuals with poor dietary habits or conditions that affect nutrient absorption or utilization.
  • Overhydration: Excessive fluid intake or fluid retention can dilute the blood, resulting in lower BUN levels. When the blood is diluted, the concentration of urea decreases, leading to reduced BUN levels.
  • Pregnancy: BUN levels tend to be lower during pregnancy. The increased blood volume and hormonal changes during pregnancy can affect kidney function and result in decreased BUN levels.
  • Severe Liver Damage: In cases of advanced liver disease, where liver function is significantly impaired, BUN levels may be lower due to reduced urea production.

How Do You Fix Low Blood Urea Nitrogen (BUN) Levels?

Fixing low Blood Urea Nitrogen (BUN) levels involves addressing the underlying cause. Here are some general strategies that the nurse may do:

  • Addressing Nutritional Deficiencies: If malnutrition or inadequate protein intake is the cause of low BUN levels, the focus is on improving nutrition. This may involve working with a registered dietitian to develop a well-balanced diet that includes sufficient protein and other essential nutrients.
  • Managing Fluid Intake: If overhydration or excessive fluid intake is leading to diluted blood and low BUN levels, it's important to regulate fluid intake. This may involve reducing fluid intake to a normal and appropriate level and addressing any underlying conditions causing fluid retention.
  • Treating Liver Disease: If liver disease is the underlying cause of low BUN levels, managing and treating the liver condition becomes a priority. This may involve lifestyle modifications, medication, or, in severe cases, liver transplant evaluation.
  • Monitoring Medications: Certain medications can impact BUN levels. If a medication is causing low BUN levels, the healthcare provider may consider adjusting the dosage or exploring alternative medications.
  • Addressing Underlying Medical Conditions: In some cases, low BUN levels may be associated with underlying medical conditions. Treating and managing these conditions may help restore BUN levels to a normal range.

Monitoring BUN levels over time can help nurses diagnose and manage various conditions. It is often measured alongside other kidney function tests, such as creatinine levels, to provide a comprehensive assessment of renal health.

What is the difference between BUN and Creatinine?

BUN (Blood Urea Nitrogen) and creatinine are two common blood tests that are often evaluated together to assess kidney function and provide a comprehensive picture of renal health. While they measure different substances, their levels can provide valuable insights when interpreted together. 

BUN measures the amount of nitrogen in the blood that comes from urea, a waste product of protein metabolism. Creatinine is a waste product of muscle metabolism excreted by the kidneys.

  • Both BUN and creatinine levels are used as markers of kidney function. The kidneys play a crucial role in filtering waste products and toxins from the blood. BUN and creatinine levels can help determine how well the kidneys are functioning in their filtration and excretion processes.
  • The BUN-to-creatinine ratio is often calculated to provide additional insights. A high BUN-to-creatinine ratio may indicate dehydration or conditions that cause increased protein breakdown, such as gastrointestinal bleeding. On the other hand, a low ratio may suggest conditions affecting the kidneys' ability to excrete urea, such as impaired renal function or urinary tract obstruction.

BUN-to-Creatinine Ratio

The BUN/Creatinine ratio is a calculated value that compares the levels of Blood Urea Nitrogen (BUN) to Creatinine in the blood. It provides additional information about kidney function and can be useful in certain clinical scenarios. 

  • Purpose: The BUN/Creatinine ratio helps assess the balance between the urea nitrogen (BUN) and creatinine levels in the blood. It provides insights into the underlying factors affecting these values and helps evaluate kidney function.
  • Normal Range: The normal range for the BUN/Creatinine ratio is typically around 10:1 to 20:1. However, the specific range may vary slightly depending on the laboratory and reference values used. It's important to note that the interpretation of the ratio should consider individual patient characteristics and other clinical factors.
  • Dehydration and Fluid Status: Changes in the BUN/Creatinine ratio can indicate alterations in hydration status.
    • In dehydration, such as reduced fluid intake or excessive fluid loss, the BUN level may rise more significantly compared to creatinine, resulting in an increased ratio.
    • In overhydration or expanded fluid volume, the BUN level may not rise as much in relation to creatinine, leading to a decreased ratio.

The BUN/Creatinine ratio is a valuable tool in assessing kidney function, particularly in relation to hydration status and certain clinical conditions.

Understanding Blood Urea Nitrogen (BUN) Lab Values

As nursing students, understanding Blood Urea Nitrogen (BUN) lab values is essential for providing quality patient care and monitoring kidney function. By familiarizing ourselves with the significance of BUN levels and the conditions that can impact them, we can confidently assess and intervene in various clinical scenarios.

Whether it's recognizing the potential causes of elevated BUN levels, such as dehydration or renal impairment, or understanding the implications of low BUN levels, such as liver disease or malnutrition, our knowledge of BUN lab values equips us to be proactive caregivers.



By closely monitoring BUN levels and considering the patient's overall clinical picture, nursing students can play a vital role in early detection and intervention. This understanding enables us to collaborate effectively with the healthcare team, implement appropriate interventions, and provide the best care to our patients.

YOU CAN DO THIS!

Happy Nursing!

 
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