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Blood urea nitrogen is used to test how well your kidneys are working. Urea is a waste product produced by the liver, filtered out of the blood by the kidneys, and removed from the body in urine.
The amount of urea nitrogen in your bloodstream, in conjunction with other biomarkers, can be used as an indicator of kidney health. High levels of urea nitrogen indicate that your kidneys may not be functioning well to filter your blood.
Age and sex are factors that can affect blood urea levels. Women and children tend to have lower blood urea levels, and all individuals tend to have rising blood urea levels as they age. Women may have lower blood urea levels during the second or third trimester of their pregnancies.
You should consider a blood urea nitrogen test if your healthcare professional believes you have kidney disease or if your kidney function needs to be assessed due to chronic conditions, including diabetes and high blood pressure¹. Symptoms of kidney disease include changes to urinary function, swelling in your limbs, muscle cramps, nausea and vomiting, loss of appetite, and fatigue². It can also be used, in conjunction with other blood tests, to help diagnose other diseases, including liver damage, urinary tract obstruction, congestive heart failure, and bleeding in the GI tract.
Since kidney damage can result in elevated levels of creatinine, testing this biomarker should also be considered. See creatinine for more information.
Additional testing of kidney function may be needed if your blood urea nitrogen levels are abnormal.
The American Board of Internal Medicine considers the reference range for blood urea nitrogen to be 8–20 mg/dL³, but this may be affected by your age and is dependent on the lab you use for your test.¹
While an elevated level usually indicates poor kidney function, it can also be due to other conditions, including dehydration, obstruction of the urinary tract, congestive heart failure, and bleeding in the GI tract.
Elevated blood urea nitrogen can result from complications related to diabetes or high blood pressure, conditions that block the flow of urine, such as kidney stones, or damage to your kidneys from an infection or autoimmune disease. Additionally, factors that cause decreased blood flow to the kidneys, such as congestive heart failure or dehydration, may cause elevated blood urea nitrogen levels. To find the root cause of your elevated blood urea level, additional testing will be required.
Low levels of blood urea nitrogen can indicate a low-protein diet, severe liver damage, or malnutrition.
Staying hydrated and consuming less protein can help lower blood urea nitrogen levels.
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