Coronavirus (43) Mass asymptomatic testing of SARS-CoV-2 using lateral flow devices (cont’d)
Continued from my last blog post.
Limitation of lateral flow tests
The lateral flow test kit from Innova for detection of SARS-CoV-2 infections has been tested by Public Health England and validated by the UK government.1,2 It was initially tested among 132 candidates when the UK government were considering the use of lateral flow devices (LFDs) in mass-testing for COVID-19 in an asymptomatic population.1
The test report showed that all the tested lateral flow devices have a viral antigen detection rate of >90% at 100,000 RNA copies/ml (for comparison, only 3,600 to 10,000 copies/ml of virus in the sample is already enough to be detected by RT-PCR, which is more than ten times as sensitive). The study found a kit failure rate of 5.6% from 8951 Innova SARS-CoV-2 Antigen Rapid Qualitative Tests. The most common reason for kit failure was poor transfer of the liquid within the device from the reservoir onto the test strip. 1
The false positive rate was 0.32% from 6954 Innova tests. This means that for every 1,000 people tested, only 3 people would get a false positive result. The study also found that the sensitivity (the detection rate of positive cases) across the sampling cohort is significantly dependent on the test operator. Sensitivity of the tests performed by laboratory scientists was 78.8%, trained healthcare-workers was 70%, while the self-trained members of the public was 57.7%.1
The above study showed that the kit failure rate for the tests is not low, and they tend to give a more accurate result only if a sample with higher viral concentration is being tested and the user performing the test is well-trained. This means the overall accuracy of the lateral flow tests is generally lower among asymptomatic people who are not well-trained and who have a generally lower viral concentration.
When it comes to the real world evaluation of Innova SARS-CoV-2 Antigen Rapid Qualitative Test, the sensitivity of the test is found to be much lower than the above report. The Innova lateral flow test was used in a mass test of the population in Liverpool last November.3 By evaluation of the performance of the Innova lateral flow test against RT-PCR testing using data from 5,869 people, it was found that 60% of infected people could not be detected by the lateral flow tests. On the other hand, the test performed better for detecting cases in people with higher viral loads, with test sensitivity in this group at 66.7%.3 Similar to the result from the other study, the specificity was 99.9% in this study.1,3 This means the positive results from the lateral flow tests are highly accurate.
Based on these research studies, the general sensitivity of the lateral flow tests are 40–76%, which means that about half of infected people may be missed.1,3,4 Those carrying COVID-19 who were wrongly told they were free of the virus could transmit to more people than those who do not have the tests, due to a false sense of security. Therefore, many scientists called on the government at least to pause the rollout of rapid asymptomatic testing using the Innova tests, as they are sceptical that the lateral flow tests are able to control effectively the transmission of infection.5,6
Can the lateral flow test detect COVID-19 variants?
There has no research paper or data available yet on the efficiency of the Innova SARS-CoV-2 Antigen Rapid Qualitative Test to detect the Kent and Indian variants which are now prevalent in the UK. The planned rollouts of lateral flow tests in schools were paused because of concerns about the risk of missing cases caused by the new and more transmissible SARS-CoV-2 variants.7
Where can we get the free lateral flow test?
After reading all the information about the free of charge lateral flow test scheme, you might want to try to have one yourself. The free rapid lateral flow tests are being made available by the government in England. As long as you are in England, aged 11 or above, and have no COVID-19 symptoms, you can order one pack of lateral flow tests per day online and it will be delivered to your home. Each pack contains 7 tests.6
The tests can also be collected at local PCR test sites and most of the local pharmacies in England. It is very important to remember that the tests are just for asymptomatic people: if you have COVID-19 symptoms, you should not go outside to collect a test; instead, you should order a PCR test and self-isolate.6
Who could benefit from the free lateral flow tests?
The sensitivity of lateral flow tests are in doubt, and the usefulness of the lateral flow tests being used as a tool to control the transmission of infection is being questioned by some scientists. However, as long as the tests are repeated twice a week as suggested by the government, there is still a chance of the asymptomatic infections being detected. Therefore, the free lateral flow test scheme available in England provides certain degree of protection for the households who have members working in patient-facing or customer-facing sectors.
However, you have to remember that the test on average misses about half of the COVID-19 infectious cases, i.e. a negative result does not rule out a COVID-19 infection. If your result is negative from the lateral flow test, it is very important to still follow all the current restrictions imposed by the government.
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 for mass-testing. medRxiv. 2021; (published online Jan 26.) (preprint). https://doi.org/10.1101/2021.01.13.21249563
(Later published online in Lancet, May 29, 2021. DOI:https://doi.org/10.1016/j.eclinm.2021.100924)
2. Order coronavirus (COVID-19) rapid lateral flow tests. GOV.UK website. https://www.gov.uk/order-coronavirus-rapid-lateral-flow-tests
3. Liverpool COVID-19 community testing pilot. Interim evaluation report by the University of Liverpool. 23 December, 2020. https://www.liverpool.ac.uk/media/livacuk/coronavirus/Liverpool,Community,Testing,Pilot,Interim,Evaluation.pdf
4. RT-LAMP assay: Fail to detect positive cases more than 50% in November in Manchester. “Covid-19: Rapid test missed over 50% of positive cases in Manchester pilot. BMJ 2020; 371 doi: https://doi.org/10.1136/bmj.m4323 (Published 06 November 2020) Cite this as: BMJ 2020;371:m4323”
5.UK government must urgently rethink lateral flow test roll out, warn experts. The BMJ news, 11/01/21. https://www.bmj.com/company/newsroom/uk-government-must-urgently-rethink-lateral-flow-test-roll-out-warn-experts/
6. Covid-19: UK regulator approves lateral flow test for home use despite accuracy concerns. BMJ news, 2020; 371 doi: https://doi.org/10.1136/bmj.m4950 (Published 23 December 2020)
7. Mass testing of COVID-19: January update on lateral flow tests. UK Parliament Post, 29 January 2021. https://post.parliament.uk/mass-testing-for-covid-19-january-update-on-lateral-flow-tests/
Continued from my last blog post.
Limitation of lateral flow tests
The lateral flow test kit from Innova for detection of SARS-CoV-2 infections has been tested by Public Health England and validated by the UK government.1,2 It was initially tested among 132 candidates when the UK government were considering the use of lateral flow devices (LFDs) in mass-testing for COVID-19 in an asymptomatic population.1
The test report showed that all the tested lateral flow devices have a viral antigen detection rate of >90% at 100,000 RNA copies/ml (for comparison, only 3,600 to 10,000 copies/ml of virus in the sample is already enough to be detected by RT-PCR, which is more than ten times as sensitive). The study found a kit failure rate of 5.6% from 8951 Innova SARS-CoV-2 Antigen Rapid Qualitative Tests. The most common reason for kit failure was poor transfer of the liquid within the device from the reservoir onto the test strip. 1
The false positive rate was 0.32% from 6954 Innova tests. This means that for every 1,000 people tested, only 3 people would get a false positive result. The study also found that the sensitivity (the detection rate of positive cases) across the sampling cohort is significantly dependent on the test operator. Sensitivity of the tests performed by laboratory scientists was 78.8%, trained healthcare-workers was 70%, while the self-trained members of the public was 57.7%.1
The above study showed that the kit failure rate for the tests is not low, and they tend to give a more accurate result only if a sample with higher viral concentration is being tested and the user performing the test is well-trained. This means the overall accuracy of the lateral flow tests is generally lower among asymptomatic people who are not well-trained and who have a generally lower viral concentration.
When it comes to the real world evaluation of Innova SARS-CoV-2 Antigen Rapid Qualitative Test, the sensitivity of the test is found to be much lower than the above report. The Innova lateral flow test was used in a mass test of the population in Liverpool last November.3 By evaluation of the performance of the Innova lateral flow test against RT-PCR testing using data from 5,869 people, it was found that 60% of infected people could not be detected by the lateral flow tests. On the other hand, the test performed better for detecting cases in people with higher viral loads, with test sensitivity in this group at 66.7%.3 Similar to the result from the other study, the specificity was 99.9% in this study.1,3 This means the positive results from the lateral flow tests are highly accurate.
Based on these research studies, the general sensitivity of the lateral flow tests are 40–76%, which means that about half of infected people may be missed.1,3,4 Those carrying COVID-19 who were wrongly told they were free of the virus could transmit to more people than those who do not have the tests, due to a false sense of security. Therefore, many scientists called on the government at least to pause the rollout of rapid asymptomatic testing using the Innova tests, as they are sceptical that the lateral flow tests are able to control effectively the transmission of infection.5,6
Can the lateral flow test detect COVID-19 variants?
There has no research paper or data available yet on the efficiency of the Innova SARS-CoV-2 Antigen Rapid Qualitative Test to detect the Kent and Indian variants which are now prevalent in the UK. The planned rollouts of lateral flow tests in schools were paused because of concerns about the risk of missing cases caused by the new and more transmissible SARS-CoV-2 variants.7
Where can we get the free lateral flow test?
After reading all the information about the free of charge lateral flow test scheme, you might want to try to have one yourself. The free rapid lateral flow tests are being made available by the government in England. As long as you are in England, aged 11 or above, and have no COVID-19 symptoms, you can order one pack of lateral flow tests per day online and it will be delivered to your home. Each pack contains 7 tests.6
The tests can also be collected at local PCR test sites and most of the local pharmacies in England. It is very important to remember that the tests are just for asymptomatic people: if you have COVID-19 symptoms, you should not go outside to collect a test; instead, you should order a PCR test and self-isolate.6
Who could benefit from the free lateral flow tests?
The sensitivity of lateral flow tests are in doubt, and the usefulness of the lateral flow tests being used as a tool to control the transmission of infection is being questioned by some scientists. However, as long as the tests are repeated twice a week as suggested by the government, there is still a chance of the asymptomatic infections being detected. Therefore, the free lateral flow test scheme available in England provides certain degree of protection for the households who have members working in patient-facing or customer-facing sectors.
However, you have to remember that the test on average misses about half of the COVID-19 infectious cases, i.e. a negative result does not rule out a COVID-19 infection. If your result is negative from the lateral flow test, it is very important to still follow all the current restrictions imposed by the government.
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 for mass-testing. medRxiv. 2021; (published online Jan 26.) (preprint). https://doi.org/10.1101/2021.01.13.21249563
(Later published online in Lancet, May 29, 2021. DOI:https://doi.org/10.1016/j.eclinm.2021.100924)
2. Order coronavirus (COVID-19) rapid lateral flow tests. GOV.UK website. https://www.gov.uk/order-coronavirus-rapid-lateral-flow-tests
3. Liverpool COVID-19 community testing pilot. Interim evaluation report by the University of Liverpool. 23 December, 2020. https://www.liverpool.ac.uk/media/livacuk/coronavirus/Liverpool,Community,Testing,Pilot,Interim,Evaluation.pdf
4. RT-LAMP assay: Fail to detect positive cases more than 50% in November in Manchester. “Covid-19: Rapid test missed over 50% of positive cases in Manchester pilot. BMJ 2020; 371 doi: https://doi.org/10.1136/bmj.m4323 (Published 06 November 2020) Cite this as: BMJ 2020;371:m4323”
5.UK government must urgently rethink lateral flow test roll out, warn experts. The BMJ news, 11/01/21. https://www.bmj.com/company/newsroom/uk-government-must-urgently-rethink-lateral-flow-test-roll-out-warn-experts/
6. Covid-19: UK regulator approves lateral flow test for home use despite accuracy concerns. BMJ news, 2020; 371 doi: https://doi.org/10.1136/bmj.m4950 (Published 23 December 2020)
7. Mass testing of COVID-19: January update on lateral flow tests. UK Parliament Post, 29 January 2021. https://post.parliament.uk/mass-testing-for-covid-19-january-update-on-lateral-flow-tests/
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