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.

The BUN test is often done to check kidney function.

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

Many 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
• Aspirin (high doses)
• Bacitracin
• Carbamazepine
• Cephalosporins
• Chloral hydrate
• Cisplatin
• Colistin
• Furosemide
• Gentamicin
• Guanethidine
• 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

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.