A blood urea nitrogen (BUN) test checks kidney function by measuring how much urea nitrogen is in your blood. Urea nitrogen is a waste product from the breakdown of protein in the body. Normally, this waste is filtered by the kidneys and leaves the body through urine. Too much or too little urea nitrogen in the blood could signify kidney problems.
The BUN test is frequently done along with other tests to diagnose or monitor kidney diseases. This test can also show whether your current kidney treatments are working. Test results may also indicate liver or urinary tract issues.
The urea nitrogen test is often ordered for people who are experiencing signs and symptoms of kidney disorders. These symptoms can include:
- frequent urination
- discolored urine (bloody, dark, or foamy)
- joint pain
- bone pain
- back pain
- muscle cramping
- restless legs
- trouble sleeping
- poor appetite
- swelling (especially in the extremities)
BUN tests are also often performed as part of regular checkups, during hospital stays, or during or after treatment for conditions like diabetes.
The BUN test does not identify the cause of a high or lower than average urea nitrogen count.
The blood urea nitrogen test doesn’t require fasting or any other pre-test preparations. You just need to show up for your appointment and have some blood drawn.
To test for the blood urea nitrogen levels, your doctor will need to collect a blood sample. The sample will then be analyzed in a labratory. You may feel the prick of the needle and mild pain or throbbing after the blood test is complete.
Urea nitrogen levels between 7 and 20 milligrams per deciliter are considered normal. If your levels are higher or lower than this, your doctor will want to do additional testing to get a better picture of your overall kidney health.
High urea nitrogen counts could be caused by the following health conditions:
- heart disease, heart failure, or heart attack
- bleeding in the digestive tract
- kidney failure
- urinary tract problems, such as obstruction
Low urea nitrogen counts can be caused by liver problems, malnutrition, not eating enough protein, or overhydration.
However, even if your blood urea nitrogen levels are too low or too high, you may not necessarily have a kidney condition. Certain factors, such as dehydration, pregnancy, high or low protein intake, steroids, and aging can impact your levels without indicating a health risk.
The only risks are those associated with having blood taken. There may be bleeding, bruising, or tenderness at the site of the blood draw. In rare cases, people become lightheaded or faint after having blood drawn. Infection is always a possibility at the draw site.