BUN (Blood Urea Nitrogen)

Blood Urea Nitrogen (BUN) tests measure the amount of urea nitrogen, is a waste product formed after proteins break down in the body. Generally, BUN tests are completed alongside other tests to diagnose and monitor kidney diseases. This test also confirms if in-progress kidney treatments are working properly. Additionally, the test results can indicate potential urinary tract and liver issues.

Who Needs a BUN Test?
A BUN test is necessary for:
  • Kidney function evaluation.
  • Determining the effectiveness of peritoneal dialysis or haemodialysis treatment.
  • Diagnosing various other conditions, including urinary tract obstruction, liver damage, gastrointestinal bleeding, and congestive heart failure. Note: An abnormal BUN test does not solely confirm any of these mentioned conditions.
  • Symptoms of kidney damage, such as discoloured urine (foamy, dark or bloody), bone pain, joint pain, back pain, poor appetite, frequent urination, trouble sleeping, itchiness, swelling (in extreme cases), restless legs, fatigue, and/or muscles cramping.
How Does a Patient Prepare for the Test?

The BUN test does not require pre-test preparations or fasting. The blood sample is taken from one of the patient’s arm veins. First, an elastic band is wrapped tightly around the upper arm. The patient may feel nothing or may feel a pinch or quick sting when the needle is inserted into the arm. Though a bruise can result at the insertion point, the chances of bruising can be reduced by maintaining pressure on the site for a few minutes. 

What Does the Test Result Mean?

Elevated BUN levels are a sign of impaired kidney function. It may be because of chronic or acute kidney disease, failure, or damage. The other possible causes include a decrease in blood flow to the kidneys, dehydration, shock, congestive heart failure, recent heart attack, severe burns, or stress. In addition, some medications may also increase the BUN level.

Other causes of increased BUN concentrations are catabolism, damage of tissue from severe burns, Addison’s disease, gastrointestinal bleeding, or an increased amount of protein in the diet. Children and women may have lower BUN levels in comparison to men due to different protein processing in the body.

Low BUN levels are not common, nor necessarily cause for concern. Generally, it is seen in cases of malnutrition, severe liver disease, and in an overhydrated person, but usually the BUN test is not used to monitor or diagnose these conditions. Also, both increased and decreased BUN levels can be found in pregnant women.

Blood urea nitrogen concentration is considered normal if one of the kidneys is fully functional, even when the other kidney proves dysfunctional.


In most cases, an increase or decrease in in blood urea nitrogen levels is due to a high protein diet intake. Diets with high protein may lead to high BUN concentrations while low-protein diets result in an abnormally low BUN level. So best to follow the wel known advice to consume a well-balanced diet.