The "Blood Urea Nitrogen (BUN) test" is a common medical blood test that evaluates kidney function by measuring the amount of urea nitrogen present in a patient's blood. Nitrogen, in the form of ammonia, is produced in the liver and broken down by the body's cells. The leftover nitrogen, after being utilised by the body's cells, mixes with other components such as carbon, oxygen, and hydrogen, and becomes chemical waste products called "urea". This urea travels through the bloodstream to the kidneys, where it is filtered and subsequently removed from the body through urine. Abnormal levels of urea may indicate that the kidneys are not functioning optimally and require medical intervention. 

What is the Blood Urea Nitrogen (BUN) test?

A blood urea nitrogen test, also known as a BUN test, is a diagnostic blood test that can provide useful insight into the functioning of the kidneys. It achieves this by measuring the amount of urea nitrogen in a blood sample. The primary function of the kidneys is to filter and remove waste products from the body. When a person develops kidney disease, waste products might not be filtered properly, leading to a buildup of these substances in the blood. This buildup can result in serious health problems, such as anaemia, high blood pressure, and heart diseases.

If a blood urea test means or indicates high levels of urea, it could indicate that the kidneys are not functioning optimally. Individuals with kidney diseases may not experience symptoms initially, but undergoing a BUN test for kidneys can help identify any changes that might potentially lead to health problems down the line.

Purpose of the test

A BUN test may be recommended by a doctor or healthcare provider to diagnose or rule out certain conditions, or monitor chronic conditions such as:

• Kidney disease or damage
• Chronic conditions like diabetes and high blood pressure
• Liver damage
• Urinary tract obstruction
• Gastrointestinal bleeding
• Congestive heart failure

While some of these conditions may not be diagnosed based solely on a blood urea test, the results of this test may be considered in conjunction with other diagnostic tests to identify specific health conditions and diseases. Additionally, a BUN test can help determine the effectiveness of dialysis treatment when a patient is undergoing peritoneal dialysis or hemodialysis.

Uses of the BUN Test

The Blood Urea Nitrogen (BUN) test is a blood test that measures the level of nitrogen in the blood that comes from urea. Urea is a waste product produced in the liver during the breakdown of proteins, and it is excreted by the kidneys. The BUN test is commonly used in medical practice for various purposes. Here are some of its primary uses:

• Kidney Function Assessment: The BUN test is often used as part of a panel of tests to assess kidney function. Elevated BUN levels may indicate impaired kidney function, as the kidneys are responsible for filtering and excreting urea from the blood. However, it's important to note that while BUN is a marker of kidney function, it is not specific, and other factors can also influence BUN levels.
• Dehydration Monitoring: Dehydration can lead to an increase in BUN levels. When there is insufficient fluid in the body, the concentration of urea in the blood may rise. The BUN test can be used as an indicator of hydration status.
• Liver Function Assessment: While BUN primarily reflects kidney function, it can also be influenced by liver function. Certain liver diseases or conditions that affect protein metabolism in the liver may impact BUN levels.
• Evaluation of Protein Intake: The BUN level can be affected by the amount of protein in the diet. High protein intake or a high-protein diet can lead to elevated BUN levels.
• Monitoring Certain Medical Conditions: The BUN test is part of routine blood work and may be monitored over time to assess changes in kidney function or overall health. It is often used in conjunction with other tests, such as creatinine, to provide a more comprehensive assessment of kidney function.
• Preoperative Assessment: In some cases, the BUN test may be included in preoperative assessments to evaluate overall health and kidney function before surgery.

What does the test measure?

A BUN test may be conducted as part of a series of tests known as a 'comprehensive metabolic panel (CMP),' which can aid in diagnosing or monitoring kidney diseases or disorders. Typically, a blood urea nitrogen test measures the quantity of urea nitrogen within the bloodstream.

When should I get this test?

A blood urea test might be recommended by a healthcare provider or doctor during a routine check-up or if they suspect that the patient exhibits symptoms of kidney damage or is at risk of kidney diseases. Individuals may be at risk of developing kidney diseases if they have:

• A family history of kidney diseases
• High blood pressure
• Diabetes
• Heart diseases

Additionally, a BUN test may be performed if the patient shows symptoms of later-stage kidney damage, such as:

• More or less frequent urge to urinate than normal
• Fatigue
• Swelling in the legs and feet
• Itching
• Muscle cramps

How to prepare for the test?

Instructions may be provided by a healthcare provider before conducting a blood urea test. Typically, if only a blood urea test is being conducted, there might not be a requirement for fasting prior to taking a blood sample. However, if additional tests are planned with the blood urea test, the healthcare provider may recommend fasting for a specific duration before the test.

How is this test done?

During the BUN test, a phlebotomist may collect blood from the patient by inserting a needle into a vein and drawing blood into a vial. This procedure typically takes about five minutes. The collected sample is then sent to a laboratory for testing.

Blood Urea Nitrogen (BUN) Test Results

The interpretation of blood urea nitrogen test results is best done by a doctor. The normal range for a BUN test may vary depending on the laboratory where the sample is tested. The lab report typically provides a reference range for the BUN test, against which the patient's test results are interpreted. While abnormal results outside the reference range may not always indicate kidney disease, they can still signal suboptimal kidney function in removing waste products from the blood. The range of blood urea nitrogen levels has been given below for reference.

Blood urea nitrogen levels generally increase with age, while infants tend to have lower blood urea levels than normal. Elevated urea levels in a BUN test meaning can be attributed to various reasons, including:

• Dehydration
• High protein diet
• Certain medications
• Severe burns
• Congestive heart failure or recent heart attack
• Gastrointestinal bleeding

Conversely, unusually low urea nitrogen levels in a BUN blood test may indicate conditions such as:

• Malnutrition
• Inadequate protein intake
• Liver disease
• Overhydration
• Advanced liver diseases, including liver cirrhosis and liver failure

The root cause of elevated or diminished blood urea levels is best determined by a doctor through additional diagnostic tests, physical examination, and symptom assessment.

What might affect the test results?

Blood urea nitrogen levels might increase even if a patient's kidneys are functioning optimally, due to various factors. These factors may include:

• A high-protein diet
• Steroid use
• Dehydration
• Burn injuries
• Ageing

This is why additional kidney tests may be necessary to compare against the normal ranges. Generally, the ratio of blood urea nitrogen levels to creatinine levels provides a more reliable measure for determining kidney health.

Conclusion

The BUN test is a medical examination used to measure blood urea nitrogen levels in the blood, providing insights into kidney function. Higher or blood test low levels than normal may indicate kidney diseases or disorders, but might not be a cause for concern in many cases. Based on the BUN test and additional diagnostic kidney tests, doctors can diagnose and treat various health conditions related to the kidneys or other associated organs.

FAQs

1. Is fasting required for a BUN test?

Ans. If the BUN test is done alone, fasting may not be required. 

2. Is high BUN level treatable?

Ans. Depending on the test results, the treating doctor may recommend additional tests for diagnosing kidney diseases. Proper hydration may be effective in the treatment of high BUN levels. The doctor may recommend certain lifestyle changes or medications for treating slightly increased BUN levels.

Reference:
https://medlineplus.gov/lab-tests/bun-blood-urea-nitrogen/#:~:text=Urea%20nitrogen%20is%20a%20waste,treatment%20can%20be%20 more%20 effective.
https://www.mayoclinic.org/tests-procedures/blood-urea-nitrogen/about/pac-20384821