To help battle the COVID pandemic and identify potentially infected individuals, Antwerp Dental Group staff will each undertake a ‘lateral-flow test’ twice per week. Not all lateral flow tests are the same. Some require a swabbing of the nose and throat (as described in the video), and others such as the Innova Lateral flow test require you to swab ONLY the inside of the nose. You must follow the instructions supplied with the kit you are using!
This test involves swabbing the inside of the nose carefully and dipping the swab into an extraction medium. This extraction medium will suspend viral antigens in solution and be maintained in a dropper bottle. You will place a couple of droplets onto a lateral flow strip and capillary flow of the analyte will draw this fluid across the strip to the ‘T’ line which consists of antibodies to Covid-19 proteins, and a control line which consists of alpha IgG antibodies.
The strip consists of a nitrocellulose membrane which enables the lateral flow assay. This is a ‘rapid test’, and a result will be identified in 30 minutes. After the 30 minutes a ‘T’ line (Test line) and a ‘C’ line (Control line) is assessed. Appearance of the C line confirms the validity of the test :
- Appearance of the ‘T’ line indicates a positive test result. In this instance you will need to inform your line manager and will need to self isolate pending a PCR antibody test
- No appearance of the ‘T’ line but appearance of the ‘C’ line is indicative of a negative test result. You will report this outcome to your manager who will record the information
Lateral flow assays should only be performed in asymptomatic individuals. Symptomatic persons should self isolate and eventually receive a RT-PCR test which has a high effectiveness (sensitivity and specificity).
It is entirely possible to attain a ‘false-positive’, and a ‘false-negative’ test result with a lateral flow assay.
Lateral flow tests have been widely dismissed as not being very accurate and have ‘loosely’ been identified as being 58% effective. What does this mean ?
Lateral flow tests :
- Have a circa 48-58 % effectiveness rate in identifying Covid positive analytes when the test is performed by a lay person. The effectiveness improves with practice, and in trained individuals the effectiveness in successfully identifying Covid-positive individuals is 70%. This means that even though you test positive, there is a chance that you may not be, and unfortunately atleast 3 out of 10 individuals may test negative despite having high viral loads of COVID-19. The test has poor sensitivity and can have a poor positive predictive value when being performed by lay people, as is the case in dental practices
- Have a >90% effectiveness rate in identifying Covid-negative analytes. This means that if you test negative, it is very likely that you are negative. The test has high specificity and has good negative predictive value
Lateral flow tests therefore have tremendous value in keeping COVID negative staff at work and supporting essential health services.
- Department of Health and Social Care. Care home LFD testing of visitors guidance. 8 Dec 2020. https://www.gov.uk/government/publications/coronavirus-covid-19-lateral-flow-testing-of-visitors-in-care-homes/care-home-lfd-testing-of-visitors-guidance.
- Preliminary report from the Joint PHE Porton Down and University of Oxford SARS-CoV-2 test development and validation cell: rapid evaluation of lateral flow viral antigen detection devices (LFDs) for mass community testing. 8 Nov 2020. www.ox.ac.uk/sites/files/oxford/media_wysiwyg/UK%20evaluation_PHE%20Porton%20Down%20%20University%20of%20Oxford_final.pdf
- Lateral flow cannot rule out SARS-COV-2. https://www.bmj.com/content/371/bmj.m4787/rapid-responses