The way that these tests have been found can be viewed as biomarker discovery; however, their identification has primarily been made one at a time. Many well-known tests have been identified based on biological insight from the fields of physiology or biochemistry; therefore, only a few markers at a time have been considered. An example of biomarker discovery is the use of inulin to assess kidney function. From this process a naturally occurring molecule (creatinine) was discovered, enabling the same measurements to be made without insulin injections.