DefinitionBUN 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 NamesBlood urea nitrogenHow the test is performedA blood sample is needed. For information on how this is done, see: VenipunctureHow to prepare for the testMany 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:AllopurinolAminoglycoside antibioticsAmphotericin BAspirin (high doses)BacitracinCarbamazepineCephalosporinsChloral hydrateCisplatinColistinFurosemideGuanethidineIndomethacinMethicillinMethotrexateMethyldopaNeomycinPenicillaminePolymyxin BProbenecidPropranololRifampinSpironolactoneTetracyclinesThiazide diureticsTriamtereneVancomycinDrugs that can decrease BUN measurements include:ChloramphenicolStreptomycinHow the test will feelWhen 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 performedThe BUN test is often done to check kidney function.Normal ValuesThe normal result is generally 6 - 20 mg/dL.Note: Normal values may vary among different labs. Talk to your doctor about your specific test results.The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.What abnormal results meanHigher-than-normal levels may be due to:Congestive heart failureExcessive protein levels in the gastrointestinal tractGastrointestinal bleedingHypovolemiaHeart attackKidney disease, including glomerulonephritis, pyelonephritis, and acute tubular necrosisKidney failureShockUrinary tract obstructionLower-than-normal levels may be due to:Liver failureLow protein dietMalnutritionOver-hydrationAdditional conditions under which the test may be done include:Acute nephritic syndromeAlport syndromeAtheroembolic kidney diseaseDementia due to metabolic causesDiabetesDigitalis toxicityEpilepsyGeneralized tonic-clonic seizureGoodpasture syndromeHemolytic-uremic syndrome (HUS)Hepatorenal syndromeInterstitial nephritisLupus nephritisMalignant hypertension (arteriolar nephrosclerosis)Medullary cystic kidney diseaseMembranoproliferative GN IMembranoproliferative GN IIPrerenal azotemiaPrimary amyloidosisSecondary systemic amyloidosisWilms' tumorWhat the risks areVeins 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 bleedingFainting or feeling light-headedHematoma (blood accumulating under the skin)Infection (a slight risk any time the skin is broken)Special considerationsFor people with liver disease, the BUN level may be low even if the kidneys are normal.ReferencesClarkson MR, Friedewald JJ, Eustace JA, Rabb H. Acute kidney injury. In: Brenner BM, eds. Brenner and Rector's The Kidney. 8th ed. Philadelphia, Pa: Saunders Elsevier; 2008:chap 29.Reviewed ByReview Date: 05/30/2011David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School, Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.