Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Observational Study
. 2021 Jul 6:374:n1637.
doi: 10.1136/bmj.n1637.

Performance of the Innova SARS-CoV-2 antigen rapid lateral flow test in the Liverpool asymptomatic testing pilot: population based cohort study

Marta García-Fiñana  1 , David M Hughes  2 , Christopher P Cheyne  2 , Girvan Burnside  2 , Mark Stockbridge  3 , Tom A Fowler  3   4 , Veronica L Fowler  3 , Mark H Wilcox  5 , Malcolm G Semple  6   7 , Iain Buchan  8
Affiliations
Observational Study

Performance of the Innova SARS-CoV-2 antigen rapid lateral flow test in the Liverpool asymptomatic testing pilot: population based cohort study

Marta García-Fiñana et al. BMJ. .

Abstract

Objective: To assess the performance of the SARS-CoV-2 antigen rapid lateral flow test (LFT) versus polymerase chain reaction testing in the asymptomatic general population attending testing centres.

Design: Observational cohort study.

Setting: Community LFT pilot at covid-19 testing sites in Liverpool, UK.

Participants: 5869 asymptomatic adults (≥18 years) voluntarily attending one of 48 testing sites during 6-29 November 2020.

Interventions: Participants were tested using both an Innova LFT and a quantitative reverse-transcriptase polymerase chain reaction (RT-qPCR) test based on supervised self-administered swabbing at testing sites.

Main outcome measures: Sensitivity, specificity, and predictive values of LFT compared with RT-qPCR in an epidemic steady state of covid-19 among adults with no classic symptoms of the disease.

Results: Of 5869 test results, 22 (0.4%) LFT results and 343 (5.8%) RT-qPCR results were void (that is, when the control line fails to appear within 30 minutes). Excluding the void results, the LFT versus RT-qPCR showed a sensitivity of 40.0% (95% confidence interval 28.5% to 52.4%; 28/70), specificity of 99.9% (99.8% to 99.99%; 5431/5434), positive predictive value of 90.3% (74.2% to 98.0%; 28/31), and negative predictive value of 99.2% (99.0% to 99.4%; 5431/5473). When the void samples were assumed to be negative, a sensitivity was observed for LFT of 37.8% (26.8% to 49.9%; 28/74), specificity of 99.6% (99.4% to 99.8%; 5431/5452), positive predictive value of 84.8% (68.1% to 94.9%; 28/33), and negative predictive value of 93.4% (92.7% to 94.0%; 5431/5814). The sensitivity in participants with an RT-qPCR cycle threshold (Ct) of <18.3 (approximate viral loads >106 RNA copies/mL) was 90.9% (58.7% to 99.8%; 10/11), a Ct of <24.4 (>104 RNA copies/mL) was 69.4% (51.9% to 83.7%; 25/36), and a Ct of >24.4 (<104 RNA copies/mL) was 9.7% (1.9% to 23.7%; 3/34). LFT is likely to detect at least three fifths and at most 998 in every 1000 people with a positive RT-qPCR test result with high viral load.

Conclusions: The Innova LFT can be useful for identifying infections among adults who report no symptoms of covid-19, particularly those with high viral load who are more likely to infect others. The number of asymptomatic adults with lower Ct (indicating higher viral load) missed by LFT, although small, should be considered when using single LFT in high consequence settings. Clear and accurate communication with the public about how to interpret test results is important, given the chance of missing some cases, even at high viral loads. Further research is needed to understand how infectiousness is reflected in the viral antigen shedding detected by LFT versus the viral loads approximated by RT-qPCR.

PubMed Disclaimer

Conflict of interest statement

Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf and declare: MGF reports grants from the Engineering and Physical Sciences Research Council; DMH reports grants from the Medical Research Council (MRC); IB reports grants from the National Institute for Health Research (NIHR), during the conduct of the study; personal fees and other from AstraZeneca, personal fees from Microsoft Research, outside the submitted work; MGS reports grants from the Department of Health and Social Care (DHSC) NIHR UK, grants from MRC UK, grants from NIHR Health Protection Research Unit in Emerging and Zoonotic Infections, University of Liverpool, during the conduct of the study, and a minority shareholder in Integrum Scientific, Greensboro, NC, USA, a company that has interests in covid-19 testing but not with lateral flow technology, outside the submitted work; IEB, MGF, MGS, DMH, GB, and CPC received grant funding from the DHSC to evaluate LFT in the Liverpool pilot discussed in this article; MHW reports grants for the NIHR, during the conduct of the study. VGF, MS, and TF are employed by the DHSC who commissioned and designed the study. The views expressed in this publication are those of the authors and not necessarily those of the National Health Service or the DHSC.

Figures

Fig 1
Fig 1
Number of participants with negative and positive lateral flow test (LFT) results by quantitative reverse-transcriptase polymerase chain reaction (RT-qPCR) viral load (based on mean cycle threshold (Ct) score across three gene targets). Intervals show the 95% confidence interval for the cumulative sensitivity to detect viral loads >1, >102, >104, and >106 RNA copies/mL
Fig 2
Fig 2
Cumulative sensitivity of Innova lateral flow test (LFT) against quantitative reverse-transcriptase polymerase chain reaction (RT-qPCR) cycle threshold (Ct). Dashed orange lines show approximate viral loads (RNA copies/mL)
None
See this image and copyright information in PMC

Comment in

References

    1. Peto T, UK COVID-19 Lateral Flow Oversight Team . COVID-19: Rapid antigen detection for SARS-CoV-2 by lateral flow assay: A national systematic evaluation of sensitivity and specificity for mass-testing. EClinicalMedicine 2021; published online 30 May. 10.1016/j.eclinm.2021.100924. - DOI - PMC - PubMed
    1. Oxford University and PHE Porton Down. University of Oxford SARS-CoV-2 test development and validation cell. Preliminary report from the Joint PHE Porton Down & 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; 2020. www.ox.ac.uk/sites/files/oxford/media_wysiwyg/UK%20evaluation_PHE%20Port...
    1. Dinnes J, Deeks JJ, Berhane S, et al. Cochrane COVID-19 Diagnostic Test Accuracy Group . Rapid, point-of-care antigen and molecular-based tests for diagnosis of SARS-CoV-2 infection. Cochrane Database Syst Rev 2021;3:CD013705. - PMC - PubMed
    1. Cevik M, Tate M, Lloyd O, et al. SARS-CoV-2, SARS-CoV, and MERS-CoV viral load dynamics, duration of viral shedding, and infectiousness: a systematic review and meta-analysis. Lancet Microbe 2021;2:e13-22. - PMC - PubMed
    1. Mina MJ, Parker R, Larremore DB. Rethinking Covid-19 test sensitivity—A strategy for containment. N Engl J Med 2020;383:e120. 10.1056/NEJMp2025631 - DOI - PubMed

Publication types