Serology is the scientific study ofserum and otherbody fluids. In practice, the term usually refers to thediagnostic identification ofantibodies in the serum.[1] Such antibodies are typically formed in response to an infection (against a givenmicroorganism),[2] against other foreign proteins (in response, for example, to amismatchedblood transfusion), or to one's own proteins (in instances ofautoimmune disease). In either case, the procedure is simple.[citation needed]
Serological tests are diagnostic methods that are used to identify antibodies andantigens in a patient's sample. Serological tests may be performed to diagnoseinfections andautoimmune illnesses, to check if a person hasimmunity to certain diseases, and in many other situations, such as determining an individual'sblood type.[1] Serological tests may also be used inforensic serology to investigate crime scene evidence.[3] Several methods can be used to detect antibodies and antigens, includingELISA,[4]agglutination,precipitation,complement-fixation, andfluorescent antibodies and more recentlychemiluminescence.[5]
Inmicrobiology,serologic tests are used to determine if a person has antibodies against a specificpathogen, or to detect antigens associated with a pathogen in a person's sample.[6] Serologic tests are especially useful for organisms that are difficult toculture by routine laboratory methods, likeTreponema pallidum (the causative agent ofsyphilis), orviruses.[7]
The presence of antibodies against a pathogen in a person's blood indicates that they have been exposed to that pathogen. Most serologic tests measure one of two types of antibodies:immunoglobulin M (IgM) andimmunoglobulin G (IgG). IgM is produced in high quantities shortly after a person is exposed to the pathogen, and production declines quickly thereafter. IgG is also produced on the first exposure, but not as quickly as IgM. On subsequent exposures, the antibodies produced are primarily IgG, and they remain in circulation for a prolonged period of time.[6]
This affects the interpretation of serology results: a positive result for IgM suggests that a person is currently or recently infected, while a positive result for IgG and negative result for IgM suggests that the person may have been infected or immunized in the past. Antibody testing for infectious diseases is often done in two phases: during the initial illness (acute phase) and after recovery (convalescent phase). The amount of antibody in each specimen (antibody titer) is compared, and a significantly higher amount of IgG in the convalescent specimen suggests infection as opposed to previous exposure.[8] False negative results for antibody testing can occur in people who areimmunosuppressed, as they produce lower amounts of antibodies, and in people who receiveantimicrobial drugs early in the course of the infection.[7]
Blood typing is typically performed using serologic methods. The antigens on a person's red blood cells, which determine theirblood type, are identified usingreagents that contain antibodies, calledantisera. When the antibodies bind to red blood cells that express the corresponding antigen, they cause red blood cells to clump together (agglutinate), which can be identified visually. The person's blood group antibodies can also be identified by adding plasma to cells that express the corresponding antigen and observing the agglutination reactions.[9][6]
Other serologic methods used intransfusion medicine includecrossmatching and the direct and indirectantiglobulin tests. Crossmatching is performed before ablood transfusion to ensure that the donor blood is compatible. It involves adding the recipient's plasma to the donor blood cells and observing for agglutination reactions.[9] The direct antiglobulin test is performed to detect if antibodies are bound to red blood cells inside the person's body, which is abnormal and can occur in conditions likeautoimmune hemolytic anemia,hemolytic disease of the newborn andtransfusion reactions.[10] The indirect antiglobulin test is used to screen for antibodies that could cause transfusion reactions and identify certain blood group antigens.[11]
Serologic tests can help to diagnose autoimmune disorders by identifying abnormal antibodies directed against a person's own tissues (autoantibodies).[12] All people have different immunology graphs.[citation needed]
A 2016 research paper by Metcalf et al., amongst whom wereNeil Ferguson andJeremy Farrar, stated that serological surveys are often used byepidemiologists to determine the prevalence of a disease in a population. Such surveys are sometimes performed by random, anonymous sampling from samples taken for other medical tests or to assess the prevalence of antibodies of a specific organism or protective titre of antibodies in a population. Serological surveys are usually used to quantify the proportion of people or animals in a population positive for a specific antibody or the titre or concentrations of an antibody. These surveys are potentially the most direct and informative technique available to infer the dynamics of a population's susceptibility and level of immunity. The authors proposed aWorld Serology Bank (or serum bank) and foresaw "associated major methodological developments in serological testing,study design, andquantitative analysis, which could drive astep change in our understanding andoptimum control ofinfectious diseases."[13]
In a helpful reply entitled "Opportunities and challenges of a World Serum Bank", de Lusignan and Correa observed[14] that the
principalethical and logistical challenges that need to be overcome are the methods of obtaining specimens, howinformed consent is acquired in busy practices, and the filling in of gaps inpatient sampling.
In another helpful reply on the World Serum Bank, the Australian researcherKaren Coates declared that:[15]
Improved serological surveillance would allowgovernments,aid agencies, andpolicy writers to directpublic health resources to where they are needed most. A better understanding ofinfection dynamics with respect to thechanging patterns of global weather should inform policy measures including where to concentratevaccination efforts andinsect control measures.
In April 2020,Justin Trudeau formed theCOVID-19 Immunity Task Force, whose mandate is to carry out a serological survey in a scheme hatched in the midst of theCOVID-19 pandemic.[16][17]
