Start Date
Expiration Date
CPT Codes
Main Lab
Reference Test
ATLAS Test Code


Specimen Information


Gold, SST


1.0 ml

Transport Info

Room Temperature 7 day stability, Refrigerated 7 day stability, Frozen 1 year stability

Fasting Required?
Patient Instructions

Reference Range

6-20 mg/dL


Enzymatic Rate

Clinical Significance

Used in the diagnosis of certain renal and metabolic diseases; most widely used test for the evaluation of kidney function. Urea is synthesized in the liver from ammonia produced as a result of deamination of amino acids. This biosynthetic pathway is the chief means of excretion of surplus nitrogen by the body.The blood urea nitrogen (BUN) test is a somewhat routine test used primarily to evaluate renal (kidney) function. The test is often performed on patients with many different diseases.Urea is formed in the liver as the end product of protein metabolism (or degradation). During digestion, protein is broken down to amino acids. Amino acids contain nitrogen, which is removed as NH4+ (ammonium ion), while the rest of the molecule is used to produce energy or other substances needed by the cell. The ammonia is combined with other small molecules to produce urea. The urea makes its way into the blood and it is ultimately eliminated in the urine by the kidneys.Most renal diseases affect urea excretion so that BUN levels increase in the blood. Patients with dehydration or bleeding into the stomach and/or intestines may also have abnormal BUN levels. Numerous drugs also affect BUN by competing with it for elimination by the kidneys. • Greater-than-normal BUN levels may indicate: - Congestive heart failure - Excessive protein catabolism (for example, starvation) - Excessive protein ingestion - Gastrointestinal bleeding - Hypovolemia (for example, burns and dehydration) - Myocardial infarction - Renal disease (for example, glomerulonephritis, pyelonephritis, and acute tubular necrosis) - Renal failure - Shock - Urinary tract obstruction (for example, tumor, stones, and prostatic hypertrophy) • Lower-than-normal BUN levels may indicate: - Liver failure - Low protein diet - Malnutrition - Over-hydration • Additional conditions under which the test may be performed: - Acute nephritic syndrome - Alport syndrome - Atheroembolic renal disease - Chronic renal failure - Complicated UTI (pyelonephritis) - Dementia due to metabolic causes - Diabetic nephropathy/sclerosis - Digitalis toxicity - End-stage renal disease - Epilepsy - Generalized tonic-clonic seizure - Goodpasture’s syndrome - Hemolytic-Uremic Syndrome (HUS) - Hepatorenal syndrome - IgM mesangial proliferative glomerulonephritis - Interstitial nephritis - Lupus nephritis - Malignant hypertension (arteriolar nephrosclerosis) - Medullary cystic disease - Membranoproliferative GN I - Membranoproliferative GN II - Non-insulin-dependent diabetes mellitus (NIDDM) - Prerenal azotemia - Primary amyloid - Rapidly progressive (crescentic) glomerulonephritis - Secondary systemic amyloid - Wilms’ tumor Special considerations:For people with liver disease, the BUN level may be low even if the kidneys are normal.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, cephalosporins, chloral hydrate, cisplatin, furosemide, guanethidine, indomethacin, methotrexate, methyldopa, nephrotoxic drugs (for example, high-dose aspirin, amphotericin B, bacitracin, carbamazepine, colistin, gentamicin, methicillin, neomycin, penicillamine, polymyxin B, probenecid, vancomycin), propranolol, rifampin, spironolactone, tetracyclines, thiazide diuretics, and triamterene.Drugs that can decrease BUN measurements include chloramphenicol and streptomycin.