Flow-through test: Difference between revisions

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{{Short description|Type of chemical test in which a water sample flows through a system}}

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'''Flow-through tests''' or '''immunoconcentration assays'''<ref name="Bernard">{{cite journal | last1 = Bernard | first1 = Branson | name-list-style = vanc |title=Point-of-Care Rapid Tests for HIV Antibody |journal=J Lab Med |date=2003 |volume=27 |pages=288–295 |url=http://www.cdc.gov/hiv/topics/testing/resources/journal_article/J_Lab_Med_20031.htm |accessdate=3 July 2016 |url-status=unfit |archiveurl=https://web.archive.org/web/20120503112410/http://www.cdc.gov/hiv/topics/testing/resources/journal_article/J_Lab_Med_20031.htm |archivedate=May 3, 2012 }}</ref> are a type of diagnostic assay that allows users to test for the presence of a [[biomarker]], usually a specific [[antibody]], in a sample such as blood. They are a type of [[point of care]] test, a test designed to be used by a healthcare provider at patient contact. Point of care tests often allow for rapid detection of a specific biomarker without specialized lab equipment and training; this aids in diagnosis and allows therapeutic action to be initiated more quickly. Flow-through tests began development in the early 1980s and were the first type of immunostrip to be developed, although [[lateral flow test]]s have subsequently become the dominant immunostrip point of care device.<ref name="John">{{cite journal | vauthors = St John A, Price CP | title = Existing and Emerging Technologies for Point-of-Care Testing | journal = The Clinical Biochemist. Reviews / Australian Association of Clinical Biochemists | volume = 35 | issue = 3 | pages = 155–67 | date = August 2014 | pmid = 25336761 | pmc = 4204237 }}</ref>

== History ==

The first flow-through test was developed in 1985 to test for the presence of [[Human chorionic gonadotropin|beta-human chorionic gonadotropin]] in urine.<ref name="John"/><ref name="Valkirs">{{cite journal | vauthors = Valkirs GE, Barton R | title = ImmunoConcentration — a new format for solid-phase immunoassays | journal = Clinical Chemistry | volume = 31 | issue = 9 | pages = 1427–31 | date = September 1985 | doi = 10.1093/clinchem/31.9.1427 | pmid = 4028392 | url = http://www.clinchem.org/content/31/9/1427.long | url-access = subscription }}</ref>

== Principle of flow-through tests ==

Flow-through assays are by principle binding assays.<ref name="Valkirs" /> In practice, they are mostly applied to detect the interaction of an [[antibody]], as from a sample of the test subject's blood, with immobilized [[antigen]]s, resulting in the formation of an antigen-antibody complex.{{citation needed|date=July 2016}} However, other types of capture-assays are technically feasible, including small molecule capture-assays or antigen tests.<ref name="Valkirs" /> Flow-through assays for the detection of [[mycotoxins]], based on [[enzyme-linked immunosorbent assay|ELISA]], have been available since the 1980s and can be used in field analyses.<ref name="Zheng">{{cite journal | vauthors = Zheng MZ, Richard JL, Binder J | title = A review of rapid methods for the analysis of mycotoxins | journal = Mycopathologia | volume = 161 | issue = 5 | pages = 261–73 | date = May 2006 | pmid = 16649076 | doi = 10.1007/s11046-006-0215-6 | s2cid = 6667768 }}</ref>

Flow-through tests typically come in the form of cassettes divided into four parts: an upper casing, a reactive membrane panel, an absorbent panel, and a lower casing.<ref name="overview">{{cite web|title=Flow-through tests, an overview|url=http://sites.path.org/dx/rapid-dx/technologies/flow-through/|publisher=PATH|accessdate=4 July 2016}}</ref> To perform a test, a diluted sample is applied to the reactive membrane panel and flows through to the absorbent pad, with the target analyte being captured in the membrane.<ref name="overview"/><ref name="works">{{cite web|title=Flow-through: how it works|url=http://sites.path.org/dx/rapid-dx/technologies/flow-through/how-it-works/|publisher=PATH|accessdate=4 July 2016}}</ref> The membrane is then washed to remove unbound, non-target molecules, washed again with a solution containing a signal reagent, and washed again to remove unbound signal reagent.<ref name="overview"/><ref name="works"/> If the analyte was present in the original sample, then by the end of this process it should be bound to the membrane, with the signal reagent bound to it, revealing (usually visually) the presence of the analyte on the membrane.<ref name="overview"/><ref name="works"/>