The amount of a potential tRNA (adenine-N(1)-)-methyltransferase catalytic subunit TRMT61B when measured in blood serum. The trait is level of potential tRNA (adenine-N(1)-)-methyltransferase catalytic subunit TRMT61B in blood serum (OBA_2043942, an Ontology of Biological Attributes term). Also known as: blood serum potential tRNA (adenine-N(1)-)-methyltransferase catalytic subunit TRMT61B amount.