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Blood Urea Nitrogen

Results

A blood urea nitrogen (BUN) test measures the amount of nitrogen in your blood that comes from the waste product Reference urea Opens New Window.

Normal

The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

**Blood urea nitrogen (BUN)** ^{Reference 1}
Adults:	10–20 Reference milligrams per deciliter (mg/dL) Opens New Window or 3.6–7.1 Reference millimoles per liter (mmol/L) Opens New Window
Children:	5–18 mg/dL

**BUN-to-creatinine ratio** ^{Reference 1}
Adults:	6–25 with 15.5 being the best value.

High values

A high BUN value can mean kidney injury or disease is present. Kidney damage can be caused by Reference diabetes Opens New Window or Reference high blood pressure Opens New Window that directly affects the kidneys. High BUN levels can also be caused by low blood flow to the kidneys caused by Reference dehydration Opens New Window or Reference heart failure Opens New Window.
Many medicines may cause a high BUN. Be sure to tell your doctor about all the nonprescription and prescription medicines you take.
A high BUN value may be caused by a high-protein diet, Reference Addison's disease Opens New Window, tissue damage (such as from severe burns), or from bleeding in the gastrointestinal tract.
High BUN-to-creatinine ratios occur with sudden (acute) kidney failure, which may be caused by Reference shock Opens New Window or severe dehydration. A very high BUN-to-creatinine ratio may be caused by bleeding in the Reference digestive tract Opens New Window Reference Opens New Window or Reference respiratory tract Opens New Window Reference Opens New Window.

Low values

A low BUN value may be caused by a diet very low in protein, malnutrition, or severe liver damage.
Drinking excessive amounts of liquid may cause overhydration and cause a low BUN value.
Women and children may have lower BUN levels than men because of how their bodies break down protein.
A low BUN-to-creatinine ratio may be caused by a diet low in protein, a severe muscle injury called Reference rhabdomyolysis Opens New Window, pregnancy, Reference cirrhosis Opens New Window, or syndrome of inappropriate antidiuretic hormone secretion (SIADH).

By:	Reference Healthwise Staff	Last Revised: Reference August 9, 2012
Medical Review:	Reference E. Gregory Thompson, MD - Internal Medicine Reference Michael Mallea, MD - Nephrology