Blood Urea Nitrogen (BUN)

Blood Urea Nitrogen test is conducted to check the urea level in the blood. Normally, this test is done along with the creatinine test which evaluates the kidney's functioning status. Increased or decreased BUN level indicates a dysfunctional kidney or liver. This test is also called the Urea Nitrogen test or Serum Urea Nitrogen test.

How are Blood, Urea and Nitrogen related?
Ammonia is produced in the liver after the break-down of proteins used by body cells. Then, this ammonia along with hydrogen, oxygen and carbon, forms urea. The urea is circulated in the blood. When it passes through the kidneys, blood and urine gets separated. The kidneys filter the urea and other waste products from blood and urine is formed. This urine is then excreted by the body. The BUN test is an indicator of the functioning of the kidney.

How is BUN Test performed?
The patient who undergoes the BUN test is asked to abstain from protein-rich food for 24 hours, as it may increase the BUN level. A blood sample is taken from the vein in the arm. There are very little chances of bleeding or any related problems. First, an elastic band is wrapped around the upper arm to stop the blood flow through veins. Then it becomes easier to insert the needle in the vein. The skin is rubbed with alcohol before inserting the needle into the vein. A tube is attached to the needle. After collecting the blood, the band is removed. After removing the needle, a gauze pad or a cotton ball should be kept on the needled spot.

What is the need of BUN Test?
The BUN blood test is done to check if the kidneys are working properly, detect kidney diseases, if any and to check whether proper treatment is being given to the kidney disease. It is also done to check if the person is suffering from severe dehydration.

What is BUN:Creatinine Ratio?
BUN and creatinine tests are conducted together, to check for dehydration. High BUN:creatinine ratio is observed when there is severe dehydration. Blockage of the urine flow in the kidney and kidney diseases, both increase the BUN and creatinine value. The normal BUN:creatinine ratio should be between 10:1 and 20:1. The ratio should be less than 30:1 in children younger than 12 months. An increased ratio indicates dehydration, acute kidney failure, mental shock, decreased blood flow to the kidneys or congestive heart failure. On the other hand, a decreased BUN:creatinine ratio indicates malnutrition, syndrome of inappropriate antidiuretic hormone secretion (SIADH), which is sometimes found with lung diseases, cancer, diseases of the central nervous system, muscle injuries like rhabdomyolysis, bleeding in the digestive or respiratory tract and liver diseases. It can also be an indication of pregnancy.

Normal BUN Values
BUN test is an efficient method to check the working of the kidney; however, it has some limitations too. Sometimes, a small change in the BUN value occurs due to some medicines like tetracycline antibiotics, nafcillin, aminoglycosides (such as Garamycin), amphotericin B (such as Fungizone), aureomycin (Kantrex), tobramycin (Nebcin), corticosteroids, and rarely the antibiotic Chloramphenicol Chloromycetin. Noticeably, a large change in the value, indicates kidney-related problems. In case of women and children, BUN values are comparatively low because their bodies break down protein molecules. An increased BUN level is known as azotemia. A BUN value more than 100 mg/dl is a panic value.

Categories	mg/dL
Children	5-15
Pregnancy	5-12
Adult	8-23

An increased BUN level indicates the following:

• Kidney diseases caused by high BP or diabetes
• Low blood flow to the kidneys due to heart failure or dehydration
• Blockage of urine flow because of kidney stone or tumor
• Excessive intake of protein-rich food
• Bleeding in the gastrointestinal tract
• Tissue damage due to burns
• Addison's disease
• Stress, mental shock

A decreased BUN level indicates the following:

• Intake of low protein food, malnutrition
• Severe liver damage
• Impaired nutrient absorption
• Use of anabolic steroids
• Syndrome of inappropriate anti-diuretic secretion (SIADH)
• Over or excessive hydration caused by drinking excessive amounts of liquids

Patients who undergo kidney dialysis, need to check BUN and creatinine levels regularly. It is a reliable method to check the functioning of the kidney.