The amount of a leukocyte immunoglobulin-like receptor subfamily B member 4 when measured in blood serum. The trait is level of leukocyte immunoglobulin-like receptor subfamily B member 4 in blood serum (Ontology of Biological Attributes identifier OBA_2042200). Also known as: blood serum leukocyte immunoglobulin-like receptor subfamily B member 4 amount.