Serum is the clear, yellowish liquid component of blood, lymph, and other body fluids, which separates when they are allowed to clot completely. Serum is composed of blood plasma, from which fibrinogen has been removed by means of clotting.


Serum therapy involves injecting serum containing antibodies (globulins), which can destroy particular pathogens. Occasionally injected serum gives rise to an allergic reaction known as serum sickness (see below); a second injection of the same serum may induce anaphylaxis.


Serum sickness

This is a type of hypersensitivity that may develop about 10 days after injection with an antiserum of animal origin or after taking certain drugs, such as penicillins. Symptoms may include an itchy rash, joint pain, fever, and enlarged lymph nodes. In severe cases, a state that is similar to shock develops. Symptoms of serum sickness usually clear up in a few days; antihistamines may hasten recovery. In severe cases, a corticosteroid drug may be prescribed.



The branch of laboratory medicine concerned with the analysis of blood serum. Applications of serology include the diagnosis of infectious diseases by the identification of antibodies, the development of antiserum preparations for passive immunization, and the determination of blood groups in paternity testing and forensic investigations.



A term used to described serum that has undergone testing for an infection and is found to have no antibodies to the infectious organism under investigation. The term also refers to the absence of an auto-antibody (one that reacts against the body's own cells) in a specific condition. An example of this usage is the lack of rheumatoid factor that occurs in seronegative rheumatoid arthritis.



Descriptive of serum that has been tested and found to contain antibodies to the infectious organism.