Serum (blood)

Serum is a clear, yellowish coloured fluid which is part of the blood. It does not contain white or red blood cells or a clotting factor. It is the blood plasma without the fibrinogens. Serum includes all proteins not used in blood clotting (coagulation) and all the electrolytes, antibodies, antigens, hormones, and any extra substances (such as drugs and microorganisms).
The study of serum is serology. Serum is used in many medical diagnostic tests, as well as in blood typing.
Blood is centrifuged to remove cellular components. Anti-coagulated blood yields plasma containing fibrinogen and clotting factors. Coagulated blood (clotted blood) yields serum without fibrinogen, although some clotting factors remain.
Serum is an important part of the self-renewal of embryonic stem cells when combined with the cytokine leukemia inhibitory factor.