The Blood Urea Nitrogen test (BUN) test is primarily used to evaluate the kidney function of the patient. It may also be prescribed to evaluate a patient’s general health status. Urea is a waste product formed in the liver when protein is metabolized in the body. Urea is released by the liver in the blood and carried to the kidneys. Here is filtered out of the body through urine. Since this is an ongoing process a small but stable amount of urea nitrogen circulates in the blood which is not harmful. Although when the kidneys cannot perform well and fail to filter out the waste, the level of urea rises in the blood. The symptoms related to the dysfunction of kidney include frequent urination, pain while urinating, swelling in arms, legs, ankles, around eyes, joint or bone pain, and continuous fatigue.