The amount of a serine/threonine-protein phosphatase 2A 56 kDa regulatory subunit delta isoform when measured in blood serum. The trait is Ontology of Biological Attributes term OBA_2043011 (level of serine/threonine-protein phosphatase 2A 56 kDa regulatory subunit delta isoform in blood serum). Also known as: blood serum serine/threonine-protein phosphatase 2A 56 kDa regulatory subunit delta isoform amount.