blood chemistry measurement blood urea nitrogen level BUN level CMO:0000049 EFO:0004741 The level of urea in the blood in terms of nitrogen content; 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 can be found in urine, blood, and lymph. VT:0005265 blood urea nitrogen measurement clinical_measurement_ontology