A BUN (blood urea nitrogen) test measures the amount of urea nitrogen in your blood. Urea nitrogen is a waste product that forms when your body breaks down protein; it is carried in the blood and normally removed by the kidneys through urine.
A BUN test is commonly done to check how well the kidneys are working. It may be ordered as part of a routine checkup, to help monitor a kidney condition or its treatment, or to screen people at higher risk (for example, those with a family history of kidney problems, diabetes, high blood pressure, or heart disease). It is often included in a comprehensive metabolic panel (CMP).
MedlinePlus gives a general normal result of about 6 to 20 mg/dL. This is a general reference only. Normal values vary from one laboratory to another and can also differ by age and sex (BUN tends to increase with age and can vary by sex), as well as by the testing method a lab uses. The range printed on your own lab report is what applies to your result, and a single value outside the general range is not a diagnosis on its own. Talk to your provider about your specific results.
A higher-than-normal BUN may suggest the kidneys are not clearing waste as well as usual, but it can also be seen with a number of non-kidney situations. General associations MedlinePlus lists include dehydration, a high-protein diet or excess protein in the digestive tract, gastrointestinal bleeding, congestive heart failure, a recent heart attack, shock, urinary tract obstruction, certain medicines, and various kidney diseases or kidney failure. This is a general, non-exhaustive list, not a diagnosis. Only your clinician can interpret what an elevated result means for you.
A lower-than-normal BUN is less commonly a focus, but per MedlinePlus it may be seen with a low-protein diet, malnutrition, liver disease or liver failure, or overhydration (too much fluid). These are again general possible associations, not a complete list and not a diagnosis.
Reference ranges vary by laboratory, age, sex, and method — the range on your own report is what applies to you. A single value out of range doesn’t confirm any condition; your clinician interprets it alongside your symptoms, history, and other results. This page is general information, not medical advice.
General reference, not medical advice, and not a substitute for your clinician. Lab reference ranges and interpretation depend on the laboratory and on your individual situation — discuss your results with a licensed healthcare professional.