Serum/ˈsɪrəm/ Definition 1 of 2Pro Tip 1/3Medical Context Used in health and medicine, often related to testing or analysis. Doctors analyzed the patient's serum for antibodies. Pro Tip 2/3Not Synonymous While 'serum' and 'plasma' are related, they aren't exactly the same in medical terminology. Unlike plasma, serum does not contain clotting factors. Pro Tip 3/3Laboratory Procedures Usually obtained through a process called centrifugation where blood is spun at high speed. The lab technician centrifuged the blood to get the serum.