Editing ELISA (section)

==Applications==
[[File:ELISA.jpg|thumb|right|Human anti-IgG, double antibody sandwich ELISA]]

Because the ELISA can be performed to evaluate either the presence of antigen or the presence of antibody in a sample, it is a useful tool for determining [[blood plasma|serum]] antibody concentrations (such as with the [[HIV test]]<ref>{{MedlinePlusEncyclopedia|003538|ELISA/Western blot tests for HIV}}</ref> or [[West Nile virus]]). It has also found applications in the [[food]] industry in detecting potential [[food allergy|food allergens]], such as [[milk]], [[peanut]]s, [[walnut]]s, [[almond]]s, and [[egg (food)|eggs]]<ref>{{cite press release |title=Food Allergen Partnership |publisher=FDA |date=January 2001 |url=https://www.fda.gov/Food/GuidanceRegulation/GuidanceDocumentsRegulatoryInformation/Allergens/ucm106779.htm |access-date=August 20, 2015 }}</ref> and as serological blood test for [[celiac disease]].<ref>{{cite journal |last1=Sblattero |first1=D. |last2=Berti |first2=I. |last3=Trevisiol |first3=C. |last4=Marzari |first4=R. |last5=Tommasini |first5=A. |last6=Bradbury |first6=A. |last7=Fasano |first7=A. |last8=Ventura |first8=A. |last9=Not |first9=T. |title=Human recombinant tissue transglutaminase ELISA: an innovative diagnostic assay for celiac disease |journal=The American Journal of Gastroenterology |volume=95 |issue=5 |pages=1253–7 |year=2000 |doi=10.1111/j.1572-0241.2000.02018.x |pmid=10811336 |s2cid=11018740 }}</ref><ref>{{cite journal |last1=Porcelli |first1=Brunetta |last2=Ferretti |first2=Fabio |last3=Vindigni |first3=Carla |last4=Terzuoli |first4=Lucia |title=Assessment of a Test for the Screening and Diagnosis of Celiac Disease |journal=Journal of Clinical Laboratory Analysis |volume= 30|issue= 1|pages= 65–70|year=2014 |pmid=25385391 |pmc=6807240 |doi=10.1002/jcla.21816 }}</ref> ELISA can also be used in toxicology as a rapid presumptive screen for certain classes of drugs.

[[File:Elisa10.jpg|thumb|Enzyme-linked immunosorbent assay plate|right]]

The ELISA was the first screening test widely used for HIV because of its high sensitivity. In an ELISA, a person's serum is diluted 400 times and applied to a plate to which HIV antigens are attached. If antibodies to HIV are present in the serum, they may bind to these HIV antigens. The plate is then washed to remove all other components of the serum. A specially prepared "secondary antibody"—an antibody that binds to other antibodies—is then applied to the plate, followed by another wash. This secondary antibody is chemically linked in advance to an enzyme.

Thus, the plate will contain enzyme in proportion to the amount of secondary antibody bound to the plate. A substrate for the enzyme is applied, and catalysis by the enzyme leads to a change in color or fluorescence. ELISA results are reported as a number; the most controversial aspect of this test is determining the "cut-off" point between a positive and a negative result.

A cut-off point may be determined by comparing it with a known standard. If an ELISA test is used for drug screening at workplace, a cut-off concentration, 50&nbsp;ng/ml, for example, is established, and a sample containing the standard concentration of analyte will be prepared. Unknowns that generate a stronger signal than the known sample are "positive". Those that generate weaker signal are "negative".

There are ELISA tests to detect various kind of diseases, such as [[Dengue fever|dengue]], [[malaria]], [[Chagas disease]],<ref>{{Cite journal|last1=Del-Rei|first1=Rodrigo Pimenta|last2=Leony|first2=Leonardo Maia|last3=Celedon|first3=Paola Alejandra Fiorani|last4=Zanchin|first4=Nilson Ivo Tonin|last5=Reis|first5=Mitermayer Galvão dos|last6=Gomes|first6=Yara de Miranda|last7=Schijman|first7=Alejandro Gabriel|last8=Longhi|first8=Silvia Andrea|last9=Santos|first9=Fred Luciano Neves|date=2019-04-18|title=Detection of anti-Trypanosoma cruzi antibodies by chimeric antigens in chronic Chagas disease-individuals from endemic South American countries|journal=PLOS ONE|language=en|volume=14|issue=4|pages=e0215623|doi=10.1371/journal.pone.0215623|issn=1932-6203|pmc=6472793|pmid=30998741|bibcode=2019PLoSO..1415623D|doi-access=free}}</ref> [[paratuberculosis|Johne's disease]], and others.<ref>{{cite journal |last1=Griffin |first1=J. F. T. |last2=Spittle |first2=E. |last3=Rodgers |first3=C. R. |last4=Liggett |first4=S. |last5=Cooper |first5=M. |last6=Bakker |first6=D. |last7=Bannantine |first7=J. P. |title=Immunoglobulin G1 Enzyme-Linked Immunosorbent Assay for Diagnosis of Johne's Disease in Red Deer (Cervus elaphus) |journal=Clinical and Vaccine Immunology |volume=12 |issue=12 |pages=1401–9 |year=2005 |pmid=16339063 |pmc=1317074 |doi=10.1128/CDLI.12.12.1401-1409.2005 }}</ref> ELISA tests also are extensively employed for [[in vitro diagnostics|''in vitro'' diagnostics]] in [[medical laboratories]]. The other uses of ELISA include:

* detection of [[SARS-CoV-2]] antibodies in blood samples<ref>{{cite journal |last1=Dhamad |first1=AE |last2=Abdal Rhida |first2=MA |title=COVID-19: molecular and serological detection methods |journal=PeerJ |date=2020 |volume=8 |pages=e10180 |doi=10.7717/peerj.10180 |pmid=33083156|pmc=7547594 |doi-access=free }}</ref>
[[File:Fig. E. COV.jpg|thumb|Schematic flowchart: ELISA and COVID-19 doi.org/10.7717/peerj.10180]]

ELISA is as of 2023 the primary method of [[plant pathogen]] detection worldwide.<ref>{{cite journal |last1=Venbrux |first1=Marc |last2=Crauwels |first2=Sam |last3=Rediers |first3=Hans |title=Current and emerging trends in techniques for plant pathogen detection |journal=Frontiers in Plant Science |date=8 May 2023 |volume=14 |doi=10.3389/fpls.2023.1120968 |doi-access=free|pmid=37223788 |pmc=10200959 |bibcode=2023FrPS...1420968V }}</ref>