The amount of a peptidyl-prolyl cis-trans isomerase FKBP4 when measured in blood serum. The trait is level of peptidyl-prolyl cis-trans isomerase FKBP4 in blood serum (OBA_2044962, an Ontology of Biological Attributes term). Also known as: blood serum peptidyl-prolyl cis-trans isomerase FKBP4 amount.