Serum is the fluid and solute component of blood which does not play a role in clotting.
It is blood plasma without fibrinogens.
Serum includes all proteins not used in blood clotting.
All electrolytes, antibodies, antigens, hormones; exogenous substances such as drugs or microorganisms are in serum.
Serum does not contain white blood cells, red blood cells, platelets, or clotting factors.
Serum is used in numerous diagnostic tests as well as blood typing.
To obtain serum, a blood sample is allowed to clot, and the sample is then centrifuged to remove the clot and blood cells, and the resulting liquid supernatant is serum.
The serum of convalescent patients recovered from an infectious disease can be used as a biopharmaceutical in the treatment of other people with that disease: antibodies generated by the successful recovery are potent fighters of the pathogen.
Such convalescent serum is a form of immunotherapy.
Serum is also used in protein electrophoresis.