The amount of a phosphatidylcholine O-16:1_18:1 when measured in blood serum. The trait is level of Phosphatidylcholine (O-16:1_18:1) in blood serum (Ontology of Biological Attributes identifier OBA_2045120). Also known as: blood serum phosphatidylcholine O-16:1_18:1 amount, level of phosphatidylcholine O-16:1_18:1 in blood serum.