The amount of a 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 4 when measured in blood serum. The trait is level of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 4 in blood serum (OBA_2042853). Also known as: blood serum 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 4 amount.