blood urea nitrogen level serum urea nitrogen level 2011-11-02T04:24:28Z BUN level CMO:0000587 The level of urea in terms of nitrogen content found in a specific volume of serum, i.e. blood plasma from which clotting factors have been removed. The urea nitrogen level is converted to urea concentration by multiplying by 60/28 or 2.14. Urea is the chief nitrogenous end product of protein metabolism in whole blood.Urea is formed in the liver from amino acids and from ammonia compounds and is found in urine, blood, and lymph. VT:0005265 clinical_measurement_ontology mshimoyama