blood urea nitrogen (BUN) [AS, blod + Gk, ouron, urine, nitron, soda, genein, to produce] , a measure of the amount of urea in the blood. Urea forms in the liver as the end product of protein metabolism, circulates in the blood, and is excreted through the kidney in urine. The BUN, determined by a blood test, is directly related to the metabolic function of the liver and the excretory function of the kidney. Normal findings (in mg/dL) are 10 to 20 for adults, 5 to 18 for children and infants, 3 to 12 for newborns, and 21 to 40 for cord blood. In the elderly, the BUN may be slightly higher than the normal adult range. A critical value of 100 mg/dL indicates serious impairment of renal function. Also called urea nitrogen, serum urea nitrogen. Compare creatinine. See also azotemia.
