Serum is the liquid and solute component of blood that is not involved in coagulation. It can be defined as blood plasma without clotting factors or as blood with all cells and clotting factors removed. Serum includes all proteins that are not used in blood clotting; all electrolytes, antibodies, antigens, hormones; and any exogenous substances (eg, drugs or microorganisms). The serum does not contain white blood cells (leukocytes), red blood cells (erythrocytes), platelets, or clotting factors.

The study of serum is serology. The serum is used in numerous diagnostic tests and blood typing. Measuring the concentration of various molecules can be useful for many applications, such as determining the therapeutic index of a candidate drug in a clinical trial.

To obtain serum, a blood sample is allowed to clot (clot). The sample is then centrifuged to remove the clot and blood cells, and the resulting liquid supernatant is serum.

Clinical and laboratory uses

Serum from convalescent patients who successfully recover (or have already recovered) from an infectious disease can be used as a biopharmaceutical in the treatment of others with that disease because the antibodies generated by successful recovery are potent combatants of the pathogen. Said convalescent serum (antiserum) is a form of immunotherapy.

The serum is also used in protein electrophoresis, due to a lack of fibrinogen which can cause false results.

Fetal Bovine Serum (FBS) is rich in growth factors and is frequently added to growth media used for eukaryotic cell culture. A combination of FBS and the cytokine leukemia inhibitory factor was originally used to maintain embryonic stem cells, but concerns about batch-to-batch variations in FBS have led to the development of serum substitutes.

Purification strategies

Blood serum and plasma are some of the largest sources of biomarkers, either for diagnosis or therapy. Its wide dynamic range, further complicated by the presence of lipids, salts, and post-translational modifications, as well as multiple degradation mechanisms, presents challenges in analytical reproducibility, sensitivity, resolution, and potential efficacy.

For the analysis of biomarkers in blood serum samples, it is possible to do a previous separation by free-flow electrophoresis that generally consists of a depletion of the serum albumin protein. This method allows for greater penetration of the proteome by separating a wide variety of charged or chargeable analytes, ranging from small molecules to cells.

Usage note

Comme beaucoup d’autres noms de masse, le sérum peut être pluriel lorsqu’il est utilisé dans certains sens. Pour parler de plusieurs échantillons de sérum provenant de plusieurs personnes (chacune avec une population unique d’anticorps), les médecins parlent parfois de serums (the pluriel Latin, par opposition aux serums).