RE: Antigens10 Feb 2021 08:14
Did someone say antibody news is old hat. True that and just 1,100 daily tests a day.
Back to Antigen LFT viral load as was asked to validate the issue with high viral load. I refer you to the British Medical Journal
WHO says that lateral flow tests are more likely to detect positive cases when viral loads are highest and patients are most infectious—typically, one to three days before the onset of symptoms and during the first five to seven days after the onset of symptoms. WHO’s Essential Diagnostics Test states that negative results should never be used as a basis of decision making.
What about asymptomatic people?
All the studies from Public Health England and Oxford University have focused on patients with symptoms.
“Asymptomatic people have a viral load peak that looks to be, on average, lower than the viral load peak of people with symptoms, and it stays at that peak for less long,” says Mike Gill, former regional director of public health for the South East of England.
In other words, if you don’t show symptoms, you shed virus or clear virus more quickly, he says, which means that any test with a relatively low level of sensitivity (such as lateral flow tests, in comparison with PCR tests) could struggle to pick up asymptomatic infections on an “intolerable” number of occasions.
Where the tests have been used among asymptomatic people in real world settings, the reported performance has indeed been lower. In a pilot study conducted in Liverpool 60% of infected asymptomatic people went undetected, including 33% of those with high viral loads.6 Up to 21 January nearly 560 000 lateral flow tests had been done on more than 200 000 Liverpool residents, identifying 4421 people who may not have otherwise known they were likely to be infectious. Among students undergoing lateral flow tests at the University of Birmingham in December, only 3% of those who would have tested positive on PCR were detected.7
This is why WHO recommends repeat testing using lateral flow devices or preferably confirmatory testing with a PCR test after a negative lateral flow test.3
“We already knew that lateral flow tests do appear more accurate with patients who have more virus present,” says Alexander Edwards, associate professor in biomedical technology at the Reading School of Pharmacy. “It follows that they may be better suited to spotting ‘spreaders’ than identifying everyone infected.”8
The question is how to manage false negative results, he says. Are people who receive a negative test result “safe” or “safer” than they were before they were tested?
That’s a worry, particularly as lateral flow tests bought over the counter become more common, and with tests easily bought on the internet and members of the public willing to purchase them for peace of mind.
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