ex vivo blood analysis blood urea nitrogen analysis 2012-07-18T12:29:32Z A test which measures the amount of nitrogen present in the blood in the form of urea, the chief nitrogenous end product of protein metabolism. Urea is formed in the liver from amino acids and from ammonia compounds and is found in urine, blood, and lymph. BUN test JSmith MMO:0000253 measurement_method_ontology