Blood Urea Nitrogen
A blood urea nitrogen (BUN) test measures
the amount of nitrogen in your blood that comes from the waste product
urea. Urea is made when protein is broken down in your
body. Urea is made in the
liver and passed out of your body in the urine.
A BUN test is done to see how well your
kidneys are working. If your kidneys are not able to
remove urea from the blood normally, your BUN level rises.
dehydration, 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
trimester of pregnancy.
Blood urea nitrogen to creatinine ratio (BUN:creatinine)
A BUN test may be done with a blood
creatinine 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
Why It Is Done
blood urea nitrogen (BUN) test is done to:
- See if your kidneys are working
- See if your kidney disease is getting
- See if treatment of your kidney disease is
- Check for severe dehydration. Dehydration
generally causes BUN levels to rise more than creatinine levels. This causes a
high BUN-to-creatinine ratio. Kidney disease or blockage of the flow of urine
from your kidney causes both BUN and creatinine levels to go up.
How To Prepare
Do not eat a lot of meat or other
protein in the 24 hours before having a blood urea nitrogen (BUN) test.
How It Is Done
The health professional drawing blood
- Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.
- Clean the needle site with
- Put the needle into the vein. More than one needle stick
may be needed.
- Attach a tube to the needle to fill it with
- Remove the band from your arm when enough blood is
- Put a gauze pad or cotton ball over the needle site as
the needle is removed.
- Put pressure to the site and then a
How It Feels
The blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight.
You may feel nothing at all from the needle, or you may feel a quick sting or