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Why are antibody tests so unreliable?

A reliable antibody test, showing that someone has already been exposed to Covid 19 and has developed antibodies which suggest immunity, could be a ‘game changer’ when it comes to allowing society to get back to work.

Unfortunately, we still don’t have tests that are accurate enough. In some cases, tests have shown to give unacceptably high numbers of false negatives and false positive results. False positives, caused by poor specificity, mean that people go into isolation when they don’t need to. False negatives, caused by poor sensitivity, could mean infected people go back into the community spreading the virus more widely. Lots of companies which are churning out Covid 19 antibody tests are saying they are highly accurate, but when we check them we find that they are often misleading.

When it comes to antibody testing for Covid 19, there are two types of antibodies. IgM antibodies are created by the body at the early stage of infection and indicate ongoing recent infection whereas IgG antibodies are produced by the body later in the course of the disease after someone has been infected and these tests suggest someone may have been infected by the virus in the past. Yet it seems to be an uphill struggle to design reliable tests to detect IgG antibodies specific to Covid 19 infection.

One of the issues is specificity, which can create false positives. When we look for antibodies, we need to be sure that we are picking up the Covid 19 antibodies, not antibodies generated by the body’s immune system after exposure to another common coronavirus.

At the end of the day, we just need to look for the correct IgG antibodies in the bloodstream. Scientists already use tests like these to check if someone has been infected with Epstein Barr virus, Dengue and hepatitis, so it is completely within our capabilities. It’s not rocket science, but till today there is not sufficient knowledge to understand the body immune response to Covid19. For how long the body maintains its immunity against the virus…6 months, one year or more?

There are other factors as well such as varying immune response of individuals as per ones genetic makeup. Also immune response may vary as per exposure to viral load, for eg: do asymptomatic individuals or individuals with mild symptoms have similar immune response as compared to those with severe symptoms and/ or hospitalisation? The antibody tests currently in the market have not been able to address these issues. One cannot also deny whether it could simply be that bureaucracy is hindering the process and there are too many labs and companies vying with each other to find the solution.

It’s very important that we have a single sensitivity and specificity standard so that all the labs and companies working on these tests follow a common standard. At the moment, they all have different ones which make it very difficult to compare them accurately. We hope in near future the government will be able to provide a reliable antibody test or most likely an effective vaccine.

Dr Izhar Bagwan
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