Blood Urea Nitrogen

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. Urea is made when protein is broken down in your body. Urea is made in the Reference liver Opens New Window Reference Opens New Window and passed out of your body in the urine.

A BUN test is done to see how well your Reference kidneys Opens New Window Reference Opens New Window are working. If your kidneys are not able to remove urea from the blood normally, your BUN level rises. Reference Heart failure Opens New Window, Reference dehydration Opens New Window, or a diet high in protein can also make your BUN level higher. Liver disease or damage can lower your BUN level. A low BUN level can occur normally in the second or third Reference trimester Opens New Window of pregnancy.

Blood urea nitrogen to creatinine ratio (BUN:creatinine)

A BUN test may be done with a blood Reference creatinine Opens New Window test. The level of creatinine in your blood also tells how well your kidneys are working—a high creatinine level may mean your kidneys are not working properly. Blood urea nitrogen (BUN) and creatinine tests can be used together to find the BUN-to-creatinine ratio (BUN:creatinine). A BUN-to-creatinine ratio can help your doctor check for problems, such as dehydration, that may cause abnormal BUN and creatinine levels.

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