Antibody tests against coronavirus are not reliable enough in the UK for people to make decisions about whether or not they can travel who they can visit, academics warned, in the latest report to question the use of large-scale tests to influence public behavior.
About one in 10 tests will omit Covid-19 cases that could lead people to make harmful decisions, such as delaying treatment, according to a review of available studies by Cochrane, a UK-based network that assesses the health research to help drive policy.
“There is no decision [patients] it should be based on test results, “said Jon Deeks, a professor of biostatistics at the University of Birmingham and lead author of the review. Antibodies are also not known to confer immunity to the disease, he added.” We have to ask: is it doing more harm than good? “he said.
The news will be a blow to hopes that antibody tests could be used to create “immunity passports,” allowing people to carry out their daily lives without fear of infection. In March, Prime Minister Boris Johnson said these tests would be a “total game changer” and “as simple as a pregnancy test.” Neither has turned out to be true.
Antibody tests, which are based on a finger prick or drawing blood from a vein, were much better at detecting Covid-19 in people at least two weeks after the onset of symptoms, the study found.
Tests performed up to seven days after the onset of symptoms collected only 30 percent of cases, 8 to 14 days after onset identified 70 percent, and 15 to 35 days later detected more than 90 percent. However, there is no data on how well the tests work more than five weeks after the onset of symptoms, the researchers noted.
“The clearest result we have is that: Time is critical,” said Professor Deeks.
The researchers also fear that the accuracy will be lower when using tests in the community, because most studies have evaluated the accuracy in hospitalized patients. This makes it clear if they can detect lower levels of antibodies associated with milder, asymptomatic cases.
These precision concerns mean that the government’s antibody program should only be conducted for the purposes of research of the entire population, known as seroprevalence studies, and not to inform individual decision-making, the researchers said. This is because scientists can adjust limitations on test precision by looking at large data sets.
NHS England and NHS Improvement wrote to NHS trusts and pathology networks on May 25, asking them to offer antibody testing to patients and increase the capacity of thousands of samples per day.
The data “makes it very clear that most, if not all, commercially available tests are not accurate enough to warrant use outside of the healthcare setting,” said Eleanor Riley, professor of immunology and infectious diseases at the University of Edinburgh, who was not involved in the review
The results of the Cochrane study follow the publication of a letter in the British Medical Journal on Wednesday, in which a group of senior academics and clinicians expressed concern about the rapid implementation of antibody testing in England.
In the letter, consultants and virologists from across the UK said there was currently no valid clinical reason for large-scale testing, the performance of the tests had not yet been adequately evaluated, and the tests were at risk of inefficient use of scarce resources.
The Cochrane Review looked at 54 studies, most of which took place in China, and over 11,000 patient records, and focused on 25 commercially available evidence. The researchers described several major concerns about the quality of the studies they turned to, including their small size and multiple samples from the same patients.
“Methodological limitations raise questions about how reliable these figures are,” said Professor Deeks.
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In a major UK study, biomarker manufacturers did not approve of identifying the tests that had been evaluated. Professor Deeks said this posed “moral problems”.
The Department of Health and Social Care said: “We are offering antibody tests to the NHS and care staff in England, with eligible patients and care residents at the request of their physician. And we are also using antibody tests to support research studies.
“Antibody testing will improve our understanding of how coronavirus is spreading across the country, which will be vital for future decisions about virus control.”
