Blood Urea Nitrogen Testing: Everything You Need to Know

1. Blood Urea Nitrogen: Introduction to this Vital Parameter of Good Renal Health

   The incidences of chronic kidney disease or other forms of renal impairment has been on the rise in the United States. According to the CDC about 1 in 7 of all people have chronic kidney disease in various stages. A key to an effective treatment of any renal disease is the early diagnosis. ^[1]

   The Blood Urea Nitrogen test or BUN testing is the primary test to evaluate the overall health and functioning of the kidneys. This test gives the physician an idea as to the functioning of not only the kidneys but also the liver and helps in proper management of the patient.^[1]

   Blood urea testing is a diagnostic test that measures the amount of urea nitrogen in your blood. Urea is a waste product that is formed when your body breaks down protein. The kidneys filter out urea from your blood and excrete it in your urine.

   1.1 Explanation of Blood Urea Nitrogen Testing:

   As the name suggests the primary aim of this test is to measure the amount of urea and nitrogen in the blood. The amount of protein that a person eats reaches the liver where it is broken down into urea and nitrogen which is absorbed by the blood. ^[2]

   The urea present in the blood then reaches the kidneys where most of it gets filtered and eliminated from the body through urine. However, some amount of urea and nitrogen still remain in the blood which is of little clinical significance. However, if the kidneys are not functioning normally then the urea and blood is not filtered out causing a gradual buildup of urea and nitrogen in the blood. ^[2]

   1.2 Importance of Blood Urea Nitrogen Testing:

   The blood urea test is often ordered as part of a comprehensive metabolic panel, which measures a range of substances in your blood, including electrolytes, glucose, and liver enzymes. Your healthcare provider may order a blood urea test if you are experiencing symptoms such as fatigue, weakness, or shortness of breath. It can also be ordered to monitor kidney function in people with chronic kidney disease or those taking medications that can affect the kidneys. ^{[3, 4]}

2. Measurement of Blood Urea Nitrogen in Blood

   2.1 How Blood Urea Nitrogen Levels are Measured:

   The technique for measuring BUN levels in blood is pretty straightforward. A simple blood test is good enough to measure the blood urea nitrogen levels. To carry out this test a sample of blood is taken from a vein in the arm and is sent to the laboratory for an analysis. BUN levels are measured in milligrams per deciliter or mg/dL. ^[5]

   2.2 Normal Blood Urea Nitrogen Levels:

   The estimation of a normal level of BUN in children and adults are different. While in children the normal range of BUN is between 5 to 18 mg/dL. In newborns this is between 3-12 mg/dL. In people above the age of 18 the normal range of BUN is between 7 and 70 mg/dL. ^[5]

   However, there are certain factors that may affect the BUN levels in the body such as age, gender, and overall health status of the individual. It is best to take the laboratory results to the healthcare provider for best interpretation of the results. ^[5]

3. Primary Reason for Blood Urea Nitrogen Testing

   3.1 Diagnosis and Monitoring of Medical Conditions:

   Aside from liver and kidney function BUN is also quite vital in the diagnosis, treatment, and monitoring of other medical conditions like congestive heart failure and dehydration. Periodic monitoring of BUN levels is also done for checking the efficacy of certain medications that affect the kidney function most specifically diuretics. ^[6]

   3.2 Prior to Surgical Procedures:

   Sometimes physicians recommend to do a BUN testing for high-risk patients before doing a surgery just to check the status of the liver and kidneys prior to the procedure. ^[6]

4. Preparing for a Blood Urea Nitrogen Test

   4.1 Is Fasting Required Before A BUN Test:

   In most of the cases fasting is not required before going for a blood test for BUN testing. However, in special cases where the physician may also want to look at certain other parameters then fasting may be recommended before the blood test. ^[7]

   4.2 What to Avoid Prior to Blood Urea Nitrogen Test:

   There are certain medications and supplements that may alter the levels of blood urea thereby resulting in false results. The physicians may therefore ask the patient to stop these supplements and medications at least 12 hours prior to the blood test for accurate results. Thus, it is essential for the patient to inform the treating physician about all the medications supplements that he or she may be taking so that the physician can advise as to what mediations and supplements to stop prior to BUN test. ^[8]

   4.3 Stay Hydrated:

   It is recommended that the patient should be completely hydrated prior to the blood test for BUN as dehydration significantly affects the BUN levels and may lead to false results after the testing. It is best to drink in lots of water prior to going for the test and avoid being out in warm weather or intense heat just prior to the test. ^[8]

5. What Happens During a Blood Urea Test?

   5.1 How Blood Is Collected For Testing:

   Blood to test BUN levels is drawn through the traditional method of inserting a needle in the vein, mostly in the arms, and collect a sample. Before inserting the needle, the site is cleaned thoroughly with antiseptic solution.^[8]

   In some cases when a vein is not visible a tourniquet is used to make the vein more visible before taking out the blood sample. Once enough sample is obtained, pressure is then applied at the area to stop the blood from oozing out of the area. The area is then bandaged to protect the injection site from any reaction or infection.^[8]

   5.2 Potential Discomfort or Risks Associated with Blood Urea Testing

   In majority of the cases the blood test for BUN is pretty safe and straightforward. However, some people may complain of some discomfort and pain when the needle is inserted to draw blood or when a tourniquet is needed to access the vein.^[9]

   In some cases, patients may have some bruising at the site of the injection after the test. In extremely rare cases some people experience potentially serious complications like infection of any type of damage to the surrounding tissues. However, this is extremely rare and most of the patients go home immediately after giving the blood sample for the test.^[9]

6. Understanding Blood Urea Test Results

   Once the BUN testing is done it is equally important to sit with the treating physician to go through the test results and understand the implications of those results. There are certain factors which may alter the BUN results including the age, gender, and overall health status of the patient and hence these things need to be kept in mind when interpreting the results of the blood test.^[10]

   6.1 Significance of High and Low BUN Levels:

   For adults the normal BUN ranges from 7 to 20 mg/dL. Anything lower or higher than this more often than not indicates that all is not right with the patient. High levels of BUN signifies that the kidney is not functioning adequately. It may also indicate that the patient may be dehydrated or may have other medical conditions that affect the functioning of the kidney.^[10]

   A person used to a high protein diet also has high BUN levels. On the other hand, low levels of BUN indicate liver dysfunction, low levels of protein intake, and even malnutrition. At times, BUN levels may also become high due to side effects of certain medications, infections, or certain autoimmune diseases.^[10]

   6.2 Requirement of Additional Investigations

   Once abnormal BUN levels are detected on the blood test, in some cases the physician may opt to carry out further investigation to get deeper into the cause of this abnormality. This may include checking the creatinine levels to definitively diagnose renal impairment may include a creatinine test or a urinalysis which may further objectify renal impairment.^[10]

   Similarly, if the BUN levels are abnormally low further investigations may need to be carried out to get to the underlying cause. This will include liver function tests to check whether the liver is functioning normally. Other investigations may be carried out to check the protein metabolism and see whether there is any abnormality that may be causing low BUN levels.^[10]

7. Conclusion

   Blood Urea Nitrogen test is a very vital took to check the functioning of the kidneys and liver. An abnormality in the BUN levels more often than not indicates an underlying renal or liver dysfunction. It is also a factor in identifying other medical conditions like cardiac failure and dehydration which may have potentially serious complications.^{[1, 2]}

   If a person knows what to expect and how to prepare for a BUN testing it will lead to more reliable and accurate test results. A better understanding of the results of the test helps the healthcare provider in coming up with a definitive diagnosis and make the best treatment plan suited for the patient and whether any further investigations may be need to come up with a definitive diagnosis for the patient.^{[1, 2]}

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