Blood Urea Nitrogen (BUN) Test: Definition, Importance, Process, Test Results, Risks, and More
The blood urea nitrogen (BUN) test measures blood urea nitrogen to assess kidney function and hydration. It helps diagnose kidney disease, dehydration, liver issues, and more. Learn about this process, its interpretation, and its importance.
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Last updated on 3rd Jul, 2025
A BUN test, which stands for blood urea nitrogen test, checks the level of urea nitrogen in a person's blood. Urea nitrogen is a waste product of protein metabolism in the human body. It is transported through the blood and removed from the body by the kidneys through urination.
Often, this test is performed to assess the function of the kidneys, hydration status, and overall bodily function. The article covers more about this test, its purpose, importance, procedure, and potential risks.
What is the Blood Urea Nitrogen (BUN) Test?
The blood urea nitrogen (BUN) test focuses on the level of urea nitrogen present in the body. Urea nitrogen is a waste product of protein metabolism, which is supposed to be excreted through the urine.
This test is commonly prescribed to patients by their healthcare providers during annual health check-ups or regularly throughout the management of kidney diseases, diabetes and hypertension.
A normal BUN level ranges from 6 to 24 mg/dL. Low levels of BUN are an indication of the optimum performance of the kidneys.
When the kidneys are supposed to filter wastes from the blood, raised BUN levels can be an indication of poor kidney health or other concerns.
Moreover, it also gives information on the state of hydration and liver function as well as the possibility of the presence of protein imbalance in a patient.
Significance of Blood Urea Nitrogen (BUN) Test
The following are the main reasons why the blood urea nitrogen (BUN) test is performed:
Assessing Kidney Health: The blood urea nitrogen (BUN) test measures the overall ability of the kidneys to filter out the waste product. Thus, the test may help identify possible kidney disease. Elevated blood urea nitrogen (BUN) levels might be associated with chronic kidney disease (CKD) and acute kidney injury (AKI).
Detecting Liver Disease: This test can diagnose liver issues because the liver produces urea. Low blood urea nitrogen (BUN) levels may be indicative of liver disease or urea overproduction.
Checking Hydration and Fluid Balance: High blood urea nitrogen (BUN) levels may indicate dehydration or fluid imbalance.
Monitoring Chronic Diseases: The blood urea nitrogen (BUN) test is useful for the monitoring of chronic diseases such as diabetes or high blood pressure, which affect kidney function. It helps observe the changes in the health of the kidneys in the patients.
Pre-Surgery Check: Before any major surgery, the blood urea nitrogen (BUN) test is performed in order to check kidney function and thus evaluate the risks involved in surgery.
The Procedure of Blood Urea Nitrogen (BUN) Test
Here is the step-by-step process of the blood urea nitrogen (BUN) test:
Step 1: Preparation for Blood Draw
A professional uses an antiseptic to wipe the upper arm and then uses an elastic band to make the veins in the arm clearly visible. This aids in searching for a proper vein for blood sampling.
Step 2: Blood Collection
The aseptic technique is performed by using a small gauge needle to puncture the vein and obtain a small volume of blood into a test tube. The patient may feel some discomfort when the needle is inserted into the vein.
Step 3: Post-Collection Care
Once the required amount of blood is taken, the needle is pulled out, and a piece of cotton wool is pressed to stop the bleeding from the broken capillary. The sample is then sent to the laboratory for testing. It can take two to three days to get the blood urea nitrogen (BUN) test results.
Step 4: After the Test
After the test, patients can continue their regular activities without fear of side effects of anaesthesia. If the test is only for blood urea nitrogen (BUN), no additional precautions need to be taken. However, if there are more tests prescribed by the doctor, the patient may have to fast.
Side Effects Associated with a Blood Urea Nitrogen (BUN) Test
Possible side effects of a blood urea nitrogen (BUN) test include:
Bleeding in the puncture zone
Bruising in the puncture zone
Blood accumulation under the skin
Infection in the puncture zone
Tabular Representation of Blood Urea Nitrogen (BUN) Level
Here is a tabular representation of the blood urea nitrogen (BUN) level for children and adults:
| Age and Sex | Normal BUN Level (mg/dL) |
| Children between 1 and 17 years | Between 7 and 20 mg/dL |
| Adult men and individuals assigned male at birth (AMAB) | Between 8 and 24 mg/dL |
| Adult women and individuals assigned females at birth (AFAB) | Between 6 and 21 mg/dL |
Factors Affecting Blood Urea Nitrogen (BUN) Results
Here are the key factors that influence the level of blood urea nitrogen (BUN):
Age
Diet
Hydration
Medication
What is High-Level Blood Urea Nitrogen?
The high level of blood urea nitrogen (BUN) may highlight that the kidneys are not working properly. However, even if the kidneys are functioning properly, people may have high blood urea nitrogen (BUN) from the following:
Having too much protein in the diet
Inadequate water intake
Certain medicines, such as carbamazepine, methotrexate, and tetracycline
Burns on the body
Obstruction to the urinary tract that prevents urine from passing out
Stress
Heart failure
Bleeding in the stomach or intestines
What is the Low-Level Blood Urea Nitrogen?
Low levels of blood urea nitrogen (BUN) may trigger a range of health conditions that include malnutrition, liver disorder, or water intoxication in the body. Causes for low blood urea nitrogen (BUN) levels include:
A diet which is deficient in protein
Small body size
Too much hydration (excessive water intake)
Liver problem
Commonly Prescribed Medications that Elevate Blood Urea Nitrogen (BUN) Levels
Following are the noteworthy medications that can raise the blood urea nitrogen (BUN) level. Patients should inform their doctor if they intake any of these medications before the test:
Amphotericin B (AmBisome, Fungizone)
Cephalosporins, a group of antibiotics
Carbamazepine (Tegretol)
Methotrexate
Methyldopa
Furosemide (Lasix)
Spironolactone (Aldactone)
Thiazide diuretics
Vancomycin (Vancocin)
Rifampin (Rifadin)
Tetracycline (Sumycin)
How to Manage High Blood Urea Nitrogen (BUN) Levels?
High levels of blood urea nitrogen (BUN) can be managed by checking why patients have kidney problems or increased blood urea nitrogen (BUN) levels.
An effective way to lower blood urea nitrogen (BUN) levels is through diet. For those without kidney disease, too much fluid should be consumed.
When blood urea nitrogen (BUN) is high, but serum creatinine is low, there may be dehydration.
Men should consume about 13 cups (3 litres) of fluids daily, and women should have around 9 cups (2.2 litres).
Conclusion
The blood urea nitrogen (BUN) test is one of the important approaches for monitoring the function of kidneys and diagnosing several diseases. An abnormal blood urea nitrogen (BUN) level could indicate kidney failure, dehydration, liver disease, or even malnutrition.
Routine health check-ups that include blood urea nitrogen (BUN) tests are important to detect early health complications. Early treatment can be lifesaving for many kidney-related and systemic diseases.
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