Flow-through test: Difference between revisions

Revision as of 14:22, 10 March 2016

Revision as of 14:53, 10 March 2016

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'''Flow-through tests''' 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. Detection of a specific biomarker aids in the diagnosis of and allows therapeutic action to be initiated quickly. The field of applications for this technology is wide, whereas generally all applications applying [[lateral flow test]]s can be replaced by flow-through assays. Commercial applications mainly target testing for infectious disease, both by viruses (e.g. [[HIV]], [[Hepatitis C]], [[Hepatitis B]] <ref name="medmira">http://medmira.com/products</ref>

) or bacteria (e.g. [[Syphilis]]<ref name="medmira_a">http://www.medmira.com/default.asp?mn=1.21.168.169products</ref>

or [[Helicobacter pylori]] <ref name="medmira_b">http://www.medmira.com/default.asp?mn=1.21.82products</ref>).

== Applications & History ==

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In the mid to late 1990’s, a significant number of manufactures switched to newly developed lateral flow tests. However that switch did cause problems as the technology was owned by a company who took an aggressive stance to protect its IP, and have done so successfully. Other companies who did not make the switch further developed flow-through. Some of those companies such as Bio-Rad continued to use original version of the technology that dated back to the late 1980s. Other companies have evolved the technology to varying degrees.

The evolved flow-through tests have benefits that rival or exceed lateral flow technology: they can be transported and stored at room temperature for prolonged periods time and allow rapid diagnostic of multiple diseases on-site with results within minutes.<ref name="medmira_c">http://www.medmira.com/imagesproducts/multiploHBVHIVHCV/MPBICABPM0001ENMultiploHBVHIVHCVProductSheet.pdfmultiplo</ref> This makes them the preferred method in e.g. large screening campaigns but also in situations of accidental blood contact or during labour when immediate treatment of a child exposed to HIV during birth by a HIV- positive mother can significantly reduce mother-to-child transmission.<ref name="rapid-diagnostics">http://www.rapid-diagnostics.org/tech-flow.htm</ref>

== Principle of flow-through tests ==

Flow-through assays are by principle binding-assays. In practice they are mostly applied to detect the interaction of an [[antibody]],from e.g. the test-subjects blood-sample, with immobilized[[Antigen]]s resulting in the formation of an antigen-antibody complex. However, other types of capture-assays are technically feasible; this also includes small molecule capture-assays or antigen tests.<ref name="medmira_d">(http://www.medmira.com/default.asp?mn=1.25.66)products/technology</ref>

“The test-principle involves a flow of fluid containing the analyte through a porous membrane and into an absorbent pad. A second layer, or submembrane, inhibits the immediate backflow of fluids, which can obscure results. The analyte is captured on the surface of the membrane by analyte capture molecules and then visualized by the addition of analyte detection molecules. These tests can be used to detect both antibodies and antigens. To perform the test, a sample is applied to the membrane and allowed to wick through by capillary action.”.<ref name="rapid-diagnostics" /><ref name="youtube">

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Advantages of flow-through tests:

* Detection of multiple pathogens in one test – combinations of up to three pathogens e.g. HIV with Hepatitis C and B are commercially available.<ref name="medmira" />

* Instant results within minutes - up to 10x5x faster result compared to e.g. lateral flow diagnostic assays.<ref name="medmira_e">.http://www.medmira.com/imagesproducts/Product%20Brochures/Mutiplo_brochure.pdftechnology</ref>

* Speed and independence of laboratory equipment decrease costs and e.g. enable easy mass-testing.<ref name="rapid-diagnostics" />

* Sensitivity of up to 100% was reported for HIV flow-through tests.<ref name="cdc">http://www.cdc.gov/hiv/topics/testing/resources/journal_article/J_Lab_Med_20031.htm</ref>