The amount of a leucine-rich repeat and fibronectin type III domain-containing protein 1 when measured in blood serum. The trait is level of leucine-rich repeat and fibronectin type III domain-containing protein 1 in blood serum (Ontology of Biological Attributes id OBA_2042225). Also known as: blood serum leucine-rich repeat and fibronectin type III domain-containing protein 1 amount.