Health Encyclopedia

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 nitrogen

How 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 Values

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

What the risks are

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)

Special considerations

For people with liver disease, the BUN level may be low even if the kidneys are normal.

Review Date:5/15/2007
Reviewed By:Robert Mushnick, M.D., Clinical Assistant Professor, Department of Nephrology, SUNY Downstate Health Center, Brooklyn, NY. Review provided by VeriMed Healthcare Network.

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