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BUN
Definition
BUN stands for blood urea nitrogen. Urea nitrogen is what forms when protein breaks down.
A test can be done to measure the amount of urea nitrogen in the blood.
Alternative Names
Blood urea nitrogenHow the Test is Performed
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to fill with blood.
A needle is inserted into the vein, and the blood is collected in an airtight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
In infants and young children, the area is cleaned with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any continued bleeding.
How to Prepare for the Test
Some drugs affect BUN levels. Before having this test, make sure the health care provider knows which medications you are taking.
Drugs that can increase BUN measurements include:
- Allopurinol
- Aminoglycosides
- Amphotericin B
- Bacitracin
- Carbamazepine
- Cephalosporins
- Chloral hydrate
- Cisplatin
- Colistin
- Furosemide
- Gentamicin
- Guanethidine
- High-dose aspirin
- Indomethacin
- Methicillin
- Methotrexate
- Methyldopa
- Neomycin
- Penicillamine
- Polymyxin B
- Probenecid
- Propranolol
- Rifampin
- Spironolactone
- Tetracyclines
- Thiazide diuretics
- Triamterene
- Vancomycin
Drugs that can decrease BUN measurements include:
- Chloramphenicol
- Streptomycin
How the Test Will Feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the Test is Performed
The BUN test is often done to check kidney function.
Normal Results
7 - 20 mg/dl. Note that normal values may vary among different laboratories.
What Abnormal Results Mean
Higher-than-normal levels may be due to:
- Congestive heart failure
- Excessive protein levels
- Gastrointestinal bleeding
- Hypovolemia
- Heart attack
- Kidney disease, including glomerulonephritis, pyelonephritis, and acute tubular necrosis
- Kidney failure
- Shock
- Urinary tract obstruction
Lower-than-normal levels may be due to:
- Liver failure
- Low protein diet
- Malnutrition
- Over-hydration
Additional conditions under which the test may be done include:
- Acute nephritic syndrome
- Alport syndrome
- Atheroembolic kidney disease
- Dementia due to metabolic causes
- Diabetic nephropathy/sclerosis
- Digitalis toxicity
- Epilepsy
- Generalized tonic-clonic seizure
- Goodpasture syndrome
- Hemolytic-uremic syndrome (HUS)
- Hepatokidney syndrome
- Interstitial nephritis
- Lupus nephritis
- Malignant hypertension (arteriolar nephrosclerosis)
- Medullary cystic kidney disease
- Membranoproliferative GN I
- Membranoproliferative GN II
- Type 2 diabetes
- Prerenal azotemia
- Primary amyloidosis
- Secondary systemic amyloidosis
- Wilms' tumor
Risks
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks are slight but may include:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Considerations
For people with liver disease, the BUN level may be low even if the kidneys are normal.
Reviewed By: Robert Mushnick, M.D., Clinical Assistant Professor, Department of Nephrology, SUNY Downstate Health Center, Brooklyn, NY. Review provided by VeriMed Healthcare Network.
