Lateral flow assays have a wide array of applications and can test a variety of samples including urine, blood, saliva, sweat, serum, and other fluids. They are currently used by clinical laboratories, hospitals, physicians and veterinary clinics, food analysis labs and environmental testing facilities. Immediacy in obtaining results is normally the key factor in choosing this technique, although simplicity and lack of a need for formal equipment are also important factors. These features allow ICTs to be used a at-home test or in pharmacies. Because of their exceptional quality, rapid test are also used routinely in well-equipped laboratories when the demand for test is low. The broad applications of rapid test can be realized because of their simplicity accompanied by high quality analytical production. The sensitivity and specificity of these techniques tend to be comparable to those of other more complex methods, and on occasion significantly better. Other uses for lateral flow assays are food and environmental safety and veterinary medicine for chemicals such as diseases and toxins. As a result, combined tests are available for HIV. LFTs that detect
nucleic acids have been developed but are still too new to see much use.
COVID-19 testing Lateral flow assays have played a critical role in
COVID-19 testing as they have the benefit of delivering a result in 15–30 minutes. The systematic evaluation of lateral flow assays during the COVID-19 pandemic was initiated at
Oxford University as part of a UK collaboration with
Public Health England. A study that started in June 2020 in the United Kingdom, FALCON-C19, confirmed the sensitivity of some lateral flow devices (LFDs) in this setting. Four out of 64 LFDs tested had desirable performance characteristics according to these early tests; the Innova SARS-CoV-2 Antigen Rapid Qualitative Test performed moderately This describes a device for which one out of every two patients infected with COVID-19 and tested in real-world conditions would receive a
false-negative result. After closure of schools in January 2021, biweekly LFTs were introduced in England for teachers, pupils, and households of pupils when schools re-opened on March 8, 2021 for asymptomatic testing. Biweekly LFT were made universally available to everyone in England on April 9, 2021. LFTs have been used for mass testing for COVID-19 globally and complement other public health measures for COVID-19. Some scientists outside government expressed serious misgivings in late 2020 about the use of Innova LFDs for screening for Covid. According to
Jon Deeks, a professor of biostatistics at the
University of Birmingham, England, the Innova test is "entirely unsuitable" for community testing: "as the test may miss up to half of cases, a negative test result indicates a reduced risk of Covid, but does not exclude Covid". Sensitivity of antigen LFTs used in 2022 was around 70% when using realtime PCR test as the ground truth. LFTs work better in symptomatic patients than in asymptomatic ones, suggesting that the amount of virus present may be too low to detect for the LFTs in many of the false-negative cases. The specificity was quite high at 99%. It is generally agreed that antigen LFTs have a higher
limit of detection (LoD) than PCR.
Biomarkers Lateral-flow assays have also been developed for
biomarkers such as levels of a certain
protein in blood or urine. The HCG (pregnancy) test is one example. If the molecule to test for is present in healthy people at a lower level, the assay needs to have an LoD high enough to
not show positive for the healthy, reference level. An example is the blood
cardiac troponin I (cTnI) LFT, which comes in both qualitative (cTnI > 0.5 ng/L) and quantitative variants. The cTnI LFTs are not as sensitive as a typical lab test, but are sufficient to "rule in" serious cases much faster than a lab test can. Another example is the LFT for sFlt1/PlGF ratio, a predictive biomarker for
pre-eclampsia. == See also ==