blood urea analysis serum urea analysis 2012-08-08T02:12:43Z An assay which measures the amount, level or concentration of urea, the chief nitrogenous endproduct of protein metabolism, in serum, the clear liquid that separates from blood after it has clotted completely, i.e. blood plasma from which fibrinogen has been removed. JSmith MMO:0000273 Not to be used for tests which return values for "serum urea nitrogen". For that test, use MMO:0000274. measurement_method_ontology