Author: Dr Mark Ali MBBS BSc FRCS CTh, Medical Director
Recently, media outlets have been bombarded with headlines highlighting the controversy behind coronavirus rapid antibody testing kits. Hailed as the golden ticket to getting out of lockdown, companies rushed to produce rapid point-of-care tests. And people understandably rushed to access them. After all, there were reports of lots of other countries using them- some papers reported the plight of UK-based companies desperate to sell at home but having to ship them abroad instead. Yet the government would not endorse these tests, despite shipping in vast quantities for analysis. It soon became clear that these tests were not the expected panacea- the only thing worse than no test is the wrong test.
Why do we need coronavirus antibody tests?
Covid-19 is a novel virus facing a completely vulnerable population. This allowed rapid spread through health systems that are woefully unprepared. Resources for handling new cases were limited and technology raced to catch up. It was clear early on that we need antibody (serological) tests: tests that can detect an immune response to COVID-19. How many people have had COVID-19 already? How many people have had COVID-19 without realising it (asymptomatic infection)? How many people who have had COVID-19 develop an immune response? How long does this response take? Is the immune response protective? These are all really important questions for our understanding of the disease, helping us to combat its grip on our lives. Antibody tests are a crucial component for answering these.
What are coronavirus rapid testing kits?
Coronavirus rapid testing kits look and perform a bit like a pregnancy test: you take a sample (fingerprick of blood) and place it on the device, wait 15 minutes and then see if there is a positive line. In theory, this is great: they can be performed at home by the patient and the results are quick. There was even talk of obtaining these kits from Amazon and Boots. However, for a test to be of any use, it must be accurate with low levels of false negatives (sensitive) and positives (specific). It soon became apparent that these tests were neither sensitive nor specific. Indeed the UK government ordered 17.5 million tests but they were all deemed unreliable.
Why is it difficult to develop rapid antibody tests?
Of course, this takes time, huge resources and access to lots of patient samples, which lots of private companies have struggled to get. The standard medical practice would dictate waiting until diagnostics and treatments have undergone highly rigorous testing to create a firm evidence-based. However, in these unprecedented times, our approach has had to shift: we must rapidly respond to race against the virus. This means working with first iterations with the intention of upgrading as and when newer iterations are available. It’s not the model most doctors are used to. But we are used to doing substantial research, continuing our professional development to provide the absolute best care available at the time.
The controversy behind coronavirus rapid testing kits
The rapid testing kits rely on a lateral flow technique, which has been used successfully for years for “point of care” tests e.g. pregnancy and HIV tests. However, it seems that this technique has proved difficult to develop for COVID-19. The false-negative (sensitivity) and false-positive (specificity) are high. Part of this will be down to the limitations of the specific lateral flow technique. But there are also many nuances to testing that we are beginning to discover. The more we do and the more research we have, the more accurate they will become.
So why offer the test?
As health professionals, we strive to offer the best, most advanced practice available at the time. This situation is so fast-moving that there will be multiple, evolving versions of diagnostics and treatment. This is reflected in the changes to processes for authorisation. There is clearly a huge demand for tests and we want to bring the best available to meet that need. Of the utmost importance, these must be administered with the appropriate guidance. People undertaking them must be aware of their limitations and understand how to interpret them.
Should I trust rapid testing kits?
The results of all tests must be reviewed in the clinical context and in the context of the accuracy of the tests. At present, laboratory-based tests are more accurate. Rapid testing kits are still being developed as these have significant advantages. We will continue to review the latest tests to ensure we consistently offer the most accurate ones available. We will always counsel patients about their accuracy to inform consent and help patients to interpret their results.
What about lab-based antibody tests?
At the moment, lab-based antibody tests are more accurate than the rapid testing kits. That is why, once they became available, we chose to cease offering the rapid tests in favour of the latest, most accurate tests available.
These lab-based tests are carried out on a blood sample using a technique called ELISA (enzyme-based immunosorbent assay) or CLIA (chemiluminescent immunoassay). These techniques have been used for years in medicine and science with a strong evidence-based. We now have more data to enhance the process and the accuracy of these tests look excellent: sensitivity is 100% after 14 days and specificity is 99.6%.
Should I get tested for coronavirus?
There is understandably huge demand for antibody testing. An antibody test can tell you if you have been exposed to COVID-19 and produced antibodies. Based on our knowledge of previous coronaviruses and early research on COVID-19, these antibodies are likely to be protective and last for a few months if not longer. For many, this is really important to know to give some peace of mind. It also satisfies curiosity. So many people have had symptoms but were unable to get tested- was that weird headache, loss of smell and fever COVID-19? Perhaps you were exposed but didn’t get any symptoms yourself. Or perhaps you have had no symptoms but wonder if you have been an asymptomatic carrier. Many companies are using these tests as part of a risk assessment for return-to-work strategies. Importantly, we would emphasise to still follow all government guidelines and precautions even if you have a positive result.