Risks

There is very little chance of a problem from having blood sample taken from a vein.

• You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
• In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
• Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

Results

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

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.

High values

• A high BUN value can mean kidney injury or disease is present. Kidney damage can be caused by diabetes or high blood pressure that directly affect the kidneys. High BUN levels can also be caused by blockage of the urinary tract (by a kidney stone or tumor) or low blood flow to the kidneys caused by dehydration or heart failure.
• 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, Addison's disease, 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 shock or severe dehydration. A blockage in the urinary tract (such as a kidney stone) can cause a high BUN-to-creatinine ratio. A very high BUN-to-creatinine ratio may be caused by bleeding in the digestive tract or respiratory tract .

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 rhabdomyolysis, pregnancy, cirrhosis, or syndrome of inappropriate antidiuretic hormone secretion (SIADH). SIADH sometimes occurs with lung disease, cancer, diseases of the central nervous system, and the use of certain medicines.