Two consumer-focused companies (Babylon Health and Superdrug) have announced that they are now selling antibody tests for home use, consisting of an antibody sampling kit and instructions for sending this to approved laboratories for testing after use.
Prof Matthew Baylis, Chair of Veterinary Epidemiology, University of Liverpool, said:
“The two antibody tests that have become available to purchase both offer high levels of accuracy, but it is essential that the general public understand what this accuracy means for them, as potential purchasers of the tests. The Babylon test confirms that a person is positive for antibody to COVID-19 (the sensitivity) with 98.5% accuracy; and it confirms a person is negative for antibody to COVID-19 (the specificity) with 99.5% accuracy. These sound impressive but they are not 100%, implying a small percentage of people will get the wrong result. How important is this small percentage? Ironically, it depends on how many people already have antibodies (the prevalence), which we won’t know until antibody tests have been widely deployed. In its own test assessments, Public Health England has assumed one in ten of us already has antibody. If this is the case, then of a thousand purchasers who get negative results (indicating no antibody) using the Babylon test, only one or two of them is expected to be actually positive (has antibody). This margin of error is good. More concerning is that of a thousand purchasers who get positive results (indicating the presence of antibody) using the Babylon test, over forty of them (~4.4%) are expected to be negative. These individuals may believe they are immune and change their behaviour, while in fact they are not immune.
“If PHE’s estimate of prevalence is too high, then this error rate becomes more significant. If the prevalence of antibody is only 5%, then 9% of positive test results are expected to be from people who are actually negative for antibody.
“At the individual level, these numbers mean that if the prevalence of antibody is 10%, then a positive test result has a one in 20 to 25 probability of being incorrect. If the prevalence is 5%, then this probability is nearer one in ten.
“The Superdrug test offers a lower sensitivity but a higher specificity than the Babylon test. The 100% specificity implies there are no false positives; and therefore, all positive test results are ‘true’. A positive test result using the Superdrug test apparently provides certainty that the individual has developed antibody to the virus that causes COVID-19 and has therefore had the disease already.
“Importantly, these tests simply assess the presence or absence of this antibody. We do not yet know if this antibody actually confers immunity, or if there is immunity, whether it will rapidly fade and leave people susceptible to COVID-19 a second time.”
Dr Colin Butter, Associate Professor and Programme Leader in Bioveterinary Science, University of Lincoln, said:
“The test kits being advertised are not ‘at home’ pregnancy test-style devices that give an instant result: none of these have passed the specificity and sensitivity requirements laid down by Public Health England. Rather, users must take a small blood sample, by the pin prick method familiar to many diabetics, which is then sent to a laboratory for analysis. At least one of the tests on offer has recently been validated by PHE.
“These tests should give a good indication of whether an individual has been infected with COVID-19 and now has serum antibody against it. Whilst this may be an indication of functional immunity, confirmation of this is awaited from large scale studies presently underway. Until it is, individuals should not assume they are fully immune to further infection.
“The tests come at a cost that is reasonable given the processing involved, though will deter many. It is to be hoped that government-run schemes will allow a high proportion of the UK population to understand if they have been infected and now have antibodies to the virus.”
Dr Joshua Moon, Research Fellow in Sustainability Research Methods in the Science Policy Research Unit, University of Sussex Business School, said:
“This is a somewhat promising development. There is a claim on the Superdrug website that the test is 97.5% sensitive and 100% specific. This test will tell you whether or not you have had COVID-19. With a 100% specificity and 97.5% sensitivity the likelihood of a false positive is 0% while the likelihood of a false negative is 2.5%. So if a test returns a positive, then you have previously come into contact with the virus; however a negative result is not always a true negative, and you may have come into contact with the virus.
“What we don’t know at this point is whether or not the presence of antibodies for COVID-19 is fully protective against future infections. We have limited evidence of recovered cases being re-infected, but an absence of evidence is not necessarily evidence of absence.
“I’m not sure I’d use it to make personal decisions. If the test returned positive, I wouldn’t rely on antibodies being protective; whereas if the test returned negative, I wouldn’t rely on that negative being a true negative. That being said, I have the luxury of working from home so my ability to be cautious is fairly high. Whether or not you take this test as something to act on will depend on the individual more than the test’s reliability.”
Prof Gino Martini, Royal Pharmaceutical Society Chief Scientific Officer, said:
“Any antibody test at present can only provide a partial picture. The real issue is that no-one knows the level of immunity that is conferred by having antibodies to coronavirus, how long it might last, and if you can become re-infected. We need much more information and data on immunity before we can understand the importance of having antibodies to the virus.”
Prof Adam Finn, Professor of Paediatrics, University of Bristol, said:
“Like many other academic labs, we in Bristol are developing diagnostic antibody tests. It is already very clear to everyone working in this field that blood from some people who have not had SARS-CoV-2 infection shows a signal in some tests – so called false positives. We know this because we have blood samples taken before the pandemic when no one has been exposed to this virus that show a signal. It is also clear that people who have had the infection and tested positive by PCR make very variable amounts of antibody, especially early on. This means that test can show false negatives – that means the test says you have not been exposed to the virus when actually you have. There are at least two tests now being manufactured and sold which have been extensively checked by Public Health England and found to be reliable almost all of the time – that is they do not give false positive or false negative results. These are both tests done on blood samples in a laboratory. For other tests now becoming available we can be less sure. There is a further complication. Even a true positive result, showing real antibody response to SARS-CoV-2, may not mean that a person is completely immune to the infection and at no risk of re-infection and of infecting others. We hope that immunity following previous infection will be fully protective in this way, but we are not yet sure.
“All of this complicated information is important. If a person takes a test and gets a false positive, they may assume they have been exposed and that they have immunity when they do not. They may expose themselves to risks when they shouldn’t. If a person gets a false negative result, they may think they are at risk of infection and pose a risk to others when they really are immune and perhaps the risks are less. But most important of all, until we know how strong and long lasting immunity is after infection, it is hard to know what to do about the results of these tests, even if the tests are reliable.
“So the bottom line is: don’t spend money and time on any test unless you have a very clear idea of what the result does or does not mean for you and what you are going to do or not do if you get a positive or negative result. If the answer is that the result is not going to change what you do because you can’t be sure what it means, then there’s no point in doing the test.”
Dr Robert Shorten, Chair, Microbiology Professional Committee, Association for Clinical Biochemistry, said:
“These are ‘home lancet collection kits’, i.e. finger prick devices to collect blood into a small tube at home that can then be posted off to a lab to be tested with (hopefully) a Public Health England (PHE) approved antibody test. Although it is hoped that the antibody tests will tell us who has been infected with SARS-CoV-2 (the virus that causes COVID-19) the main utility of these tests is for surveillance; to give us an idea of the number of people infected. The NHS and PHE are planning how to roll these tests at scale in accredited laboratories with skilled healthcare scientists to maximum public health effect. Linking these results to the public health system will help with understanding the epidemiology of the infection.
“If laboratory-based antibody tests are being used, then the cost of the test alone (excluding staff, etc.) would be in the region of a few pounds. A positive result would suggest that an individual has been infected with SARS-CoV-2 at some point in the past. It is not yet clear if a positive result would suggest immunity to further infection, and if it does, for how long the immunity would last. As with all tests, there is a risk of false negative and false positive results and we still have much to learn about the immune response in COVID-19.
“Therefore antibody test results are most helpful if linked to the public health system to inform public health policy rather than as peace of mind for the individual.”
Prof Stephen Evans, Professor of Pharmacoepidemiology, London School of Hygiene & Tropical Medicine, said:
“It is important to distinguish between “Home Sampling” kits, which is what the current products are, and “Home testing” kits, which these are not. The sampling kits allow for blood samples to be taken at home, without medical supervision, and for the blood samples to be sent off to a certified laboratory where the samples will be tested and then the results returned to the patients.
“Currently the MHRA refers to “Home Sampling” kits but only has any remarks about saliva or throat swab sampling. It has no remarks about blood sampling.
“The MHRA say no “Home testing” kits have been approved, but these would be ones that did not require samples to be sent off to a lab for testing, as is the case for the currently available kits. They would be analogous to home pregnancy tests where the result is available to the patient without any need for a sample to be sent away.
“Everyone should be aware of the distinction between “Home sampling” and “Home testing” kits.
Will these tests be reliable and how we can know that for sure?
“To be marketed the sampling kits must have a CE mark, but the test has to be done in a certified laboratory and this will provide reliable results if instructions are followed carefully. The reality is likely to be that some will not follow the instructions and the reliability in such circumstances are unknown.
What will one of these tests tell people who take it and how useful will that be?
“It will tell people whether they have antibodies to the SARS-CoV-2 virus. It is expected that will be an indicator of at least some level of immunity, but that is currently unknown.
“The sampling kit providers make this clear on their website – for example, one says:
‘Am I immune if my test is positive?
‘Whether antibodies mean immunity is still unclear. If you have antibodies, then it is thought that you might have some level of immunity to coronavirus. But without further research or conclusive data, we should assume it does not.
‘Research on past virus outbreaks has shown that even people with antibodies can get infected again within a year. If you do have immunity, it’s also not clear how long that immunity will last.’
“This is a very clear statement. They also make it clear that the test does not indicate if the virus is currently present because it can take 21 days (according to one of the kit providers, while another suggests 14 days) for antibodies to be detectable after an infection starts.
“The test is probably useful for those who think they may have had COVID-19 with either no or very mild symptoms and did not have a previous test for the virus. It will give an indicator of their likely immunity, but as they say it is not a guarantee against having another infection with SARS-CoV-2.
Where do these tests fit in with the government antibody tests we have been promised will be available shortly – should people wait or doesn’t it matter?
“We do not have details of the “government tests” as far as I know and so it is an individual decision, rather like paying for a flu vaccine or getting one on the NHS. It is likely that they will have similar reliability. The decision as to whether to return to work is likely to be influenced by, but not determined by, the result of one of these tests. The high specificity, which means a very low false positive rate is good. One of the companies states,
‘out of 1000 people that haven’t had coronavirus, 5 will receive a positive result’
“While another says,
‘The test will never give a ‘false positive’ result – there’s no way it will say that you have COVID-19 antibodies if you do not have them.’
“This seems rather a strong claim since to be absolutely sure (“never”), an infinite number of people will have to have been tested.”
Dr Simon Clarke, Associate Professor in Cellular Microbiology, University of Reading, said:
“When someone falls ill with COVID-19, their immune system generates a range of antibodies which recognise various bits of the coronavirus. It’s not yet known which, if any, of these protect us against subsequent infection, but having these antibodies is a reliable way of confirming that someone has been infected previously. Their presence does not indicate that someone is immune, and it should be remembered that any post-infection immunity may dwindle rapidly.
“These tests are good for satisfying people’s curiosity, but no more. We just don’t know enough about what it takes to make someone immune to COVID-19 to accurately test people.”
Prof Martin Hibberd, Professor of Emerging Infectious Disease, London School of Hygiene & Tropical Medicine, said:
“These new at home tests promise to be quite popular, as people who have not had the opportunity to be tested wonder if they have had the disease. However, these tests have not been evaluated in the format that they are being used (finger prick at home and posting to a laboratory for reading) so we cannot yet be confident in their sensitivity and specificity.
“Despite this, I am pleased to see that the process includes a laboratory approach to reading the test, which should reduce the errors associated with doing this at home. And of course, a finger prick test at home is easier than visiting a clinic to give a more regular blood sample.
“The problem with these tests will come with their interpretation in the wider context of preventing COVID-19 and SARS-CoV-2 transmission. A positive result shows that you have had the infection, but we do not yet know how likely that means you are to be protected from future infections, or how long those antibodies will last. And of course, even if protected, you may still be able to transmit the disease by spreading the virus from one surface to another, for example by touching door handles. People using this test will need to interpret the result with caution and still follow guidelines on transmission prevention.”
Dr Alexander Edwards, Associate Professor in Biomedical Technology, Reading School of Pharmacy, University of Reading, said:
“It is clear that antibody tests are finally becoming more widely available; it takes this long to collect enough samples to fully evaluate such tests because you need carefully collected samples from people who recovered long enough ago to have fully developed the antibody response, and these people must have had a positive swab/RT-PCR test.
“On the type of test: one important point is for people to understand that this is not a home test – instead, it is home sampling. This is not going to be a “pregnancy tester” style test that you use at home. Users have to take a blood sample at home, and then send this sample to the lab. I would expect the laboratory test will be similar to the Roche and Abbott tests which have recently been evaluated by PHE. We now know the performance of such tests and they typically have high specificity, but sensitivity varies.
“On the test performance: we don’t yet have a lot of published data comparing samples taken at home vs samples taken at a clinic for COVID-19, but prior work on other infections (e.g. home HIV testing) have shown that it is usually possible to get a test result from a sample taken at home. If there is a problem with the blood sample taken at home, it is possible the lab won’t be able to return a result. For example, if there isn’t enough blood, the lab won’t be able to process the sample. Using the lancets is not straightforward, and often it’s hard to get enough blood – some people really don’t like blood either!
“Another really important point is that these tests become more sensitive the longer after infection. So if you had symptoms in the last week or two, there is a lower chance that you have enough antibody to be detected. If you were infected more than 20 days ago, it is increasingly likely the test will be positive – and some initial studies with small numbers of samples suggest the test can approach 100% sensitivity at later timepoints. If you put together the need to wait long enough after symptoms, the lack of published data comparing home sampling vs blood sample taken by professional, it is important that people understand we don’t yet know exactly how accurate this antibody testing service will be. The published accuracy will have some caveats and will represent the performance with very carefully defined sample sets.
“On the usefulness of these tests: as we’ve repeatedly heard (for example from WHO), testing positive with an antibody test should not be taken to mean you are immune. Although people are unlikely to become re-infected, we don’t know how long immunity lasts or how well antibody levels predict immunity, and so it’s vital that people don’t assume that a positive test result automatically makes them ‘safe’, both for their own health and for the health of others. I have also heard it being suggested that workers could take an antibody test and if that were negative, be cleared to work. This is NOT safe because it’s perfectly possible to be actively infected with COVID-19 (and infectious) but have a negative antibody test because it can take weeks for the antibody to be detectable. At the moment, the biggest benefits of antibody testing are in mapping spread (who was infected where?) and for vaccine development; it’s not clear how personal testing will fit this.
“The most important message therefore is people should be fully educated about what the test would mean for them, and whether there is any benefit to purchasing a test.
“Overall this is great news, and I hope this situation will stimulate much more use of home testing, not just for COVID-19 but for other health conditions. Just as we have seen a big increase in remote consultations with GPs, it would be great to see wider availability of home sampling and home testing.”
Prof Will Irving, Professor of Virology, University of Nottingham, said:
“There are a number of antibody tests becoming available commercially. Each kit will claim very high (e.g. >97%) sensitivity and even higher (maybe 100%) specificity. Whilst these figures are very reassuring, there are one or two caveats to bear in mind. The sensitivity data will be dependent on what kind of serum samples have been tested. If these are mostly – or all – from hospitalised patients, then the figure may be an overestimate, as there are data suggesting that individuals who don’t become very ill with COVID-19 may not make very high levels of antibody. It is often difficult to assess the extent to which any manufacturer has included serum samples from mildly or asymptomatic cases of proven infection in their sensitivity analysis. The same is true of specificity – whilst most kits will have been tested against serum samples known to contain high levels of antibodies to other viruses such as influenza virus, it may not be clear if the manufacturers have tested samples known to contain high levels of antibodies to other human coronaviruses, which are more likely to give rise to cross-reactivity (and hence lower the specificity).
“Aside from the above caveats, a positive result is an indication that the individual has been infected at some time in the past, but the manufacturers are correct in indicating that this doesn’t necessarily indicate protection against future re-infection. The main use of these assays will be to assess the level of population exposure to the virus, and that sort of data is extremely valuable for the mathematical models of how the virus is spreading (or not).
“The idea of getting the individuals to take their own sample and then post it to the laboratory is a good one and will encourage uptake.”
Prof Lawrence Young, Professor of Molecular Oncology, University of Warwick, said:
Will these tests be reliable and how we can know that for sure – what does PHE approval mean in this context?
“A position statement from PHE regarding COVID-19 tests states that ‘It should be noted that PHE is not a regulatory body and that PHE does not issue accreditation of any testing laboratories or provide approvals, validations or endorsements of any particular products including any COVID-19 diagnostic assay.’
What will one of these tests tell people who take it and how useful will that be?
“It will tell people whether they have had a past infection with SARS-CoV-2 and whether they have antibodies. But we still don’t know whether these antibodies provide any protection from re-infection. So there is the possibility of false reassurance.
Where do these tests fit in with the government antibody tests we have been promised will be available shortly – should people wait or doesn’t it matter?
“The government have evaluated two different commercial antibody tests and are currently rolling out the Roche test to hospital laboratories. These will be useful for identifying who has previously been infected and for assessing the degree of previous infection in the community. I assume that there will be some prioritisation in these tests so that they won’t be generally available.
Would you personally buy, take, or rely on one of these tests to make decisions about whether to return to work, etc?
Are the press releases for these tests accurate?
“They look ok but what about clinical governance? It might worry people if they have a positive test and they’d need to notify their GP. What is the ‘correct counselling and medical support’ they mention in one of the press releases? They highlight that a positive antibody test result does not confer immunity and shouldn’t impact current precautions such as social distancing. So why take the test in the first place? What value does it provide?
One of these tests is listed as costing £69 – what are your thoughts on this?
All our previous output on this subject can be seen at this weblink:
Prof Matthew Baylis: No interests to declare
Dr Colin Butter: No interests to declare
Prof Gino Martini: No interests to declare
Prof Adam Finn: No conflicts of interest
Dr Rob Shorten: No interests to declare
Prof Stephen Evans: No conflicts of interest
Dr Simon Clarke: No interests to declare
Dr Alexander Edwards: “I have shares in a diagnostic technology company that I co-founded and am director of (Capillary Film Technology), but it does not sell any antibody testing products. It is only developing testing technology and some research only diagnostic use.”
Prof Will Irving: No interests to declare
Prof Lawrence Young: No interests to declare
None others received