The amount of a 5-hydroxymethyl-dUMP N-hydrolase when measured in blood serum. The trait is Ontology of Biological Attributes id OBA_2043219 (level of 2'-deoxynucleoside 5'-phosphate N-hydrolase 1 in blood serum). Also known as: blood serum 5-hydroxymethyl-dUMP N-hydrolase amount.