The amount of a RNA polymerase II subunit A C-terminal domain phosphatase SSU72 when measured in blood serum. The trait is level of RNA polymerase II subunit A C-terminal domain phosphatase SSU72 in blood serum (Ontology of Biological Attributes term OBA_2043668). Also known as: blood serum RNA polymerase II subunit A C-terminal domain phosphatase SSU72 amount.