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.
Heart failure , 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. 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.
A BUN-to-creatinine ratio can help your doctor check for problems, such as dehydration, that may cause abnormal BUN and creatinine levels. When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch. There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.
Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. Afterward, the site may be sore. Your BUN levels might rise even if your kidneys are working as they should for many reasons.
These include:. This is why the ratio of BUN levels to creatinine levels is a more reliable measure of kidney health. You don't need to prepare for this test. Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. Search Encyclopedia. Blood Urea Nitrogen Does this test have other names? Why do I need this test?
Symptoms that can mean kidney problems include: Needing to urinate more or less often Joint or bone pain Muscle cramps Restless legs while you're trying to sleep Fatigue Itchiness Swelling in the arms or legs Many people with kidney problems may not have symptoms right away.
What other tests might I have along with this test? More Information Diabetic coma. Request an Appointment at Mayo Clinic. Share on: Facebook Twitter. Show references Mayo Clinic Laboratories. Blood urea nitrogen BUN , serum. Accessed April 17, Rodwell VW, et al. In: Harper's Illustrated Biochemistry. McGraw-Hill Education; Lab Tests Online. Blood urea nitrogen. Kidney disease adult.
Mayo Clinic; After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.
You don't need any special preparations for a BUN test. If your health care provider has also ordered other blood tests, you may need to fast not eat or drink for several hours before the test.
Your health care provider will let you know if there are any special instructions to follow. There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
Normal BUN levels can vary, but generally a high level of blood urea nitrogen is a sign that your kidneys are not working correctly. However, abnormal results don't always indicate that you have a medical condition needing treatment. Higher than normal BUN levels can also be caused by dehydration, burns, certain medicines, a high protein diet, or other factors, including your age. BUN levels normally increase as you get older.
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