COVID-19 Anti Body Testing

Th Why Do We Need Antibody Tests for COVID-19? Diagnosing viral infections currently relies on two major methodologies: Reverse Transcription Quantitative Polymerase Chain Reaction (RT-qPCR) and serological immunoassays that detect viral-specific antibodies (IgM and IgG) or antigens. Although, RT-qPCR is a highly sensitive test for SARS-CoV-2 (the virus that causes COVID-19) it has its limitations. RT-qPCR requires high-quality nasopharyngeal swabs containing sufficient amounts of viral RNA. This can be a challenge because the amount of viral RNA not only varies tremendously between patients, it can also varies within the same patient depending on the timing of the test and the start of the infection and/or the onset of symptoms. In addition, nasopharyngeal swabs are not only very unpleasant to the patient, the sampling techniques vary significantly from nurse to nurse. Without sufficient viral RNA RT-qPCR can return a false negative test result. RT-qPCR also requires highly trained personnel to perform complex RNA extraction steps and PCR. Normally, this would not be a problem when testing a few thousand samples. RT-qPCR becomes an issue when dealing with a global pandemic with potentially millions of people to test. This leads to delays in testing as medical facilities become overwhelmed with requests. IgG/IgM serological tests offer some advantages over RT-qPCR. Firstly, serological tests detect human antibodies (proteins belonging to the immunoglobulin class) which are known to be much more stable than viral RNA. As a result, IgM/IgG serological specimens are less sensitive to spoilage during collection, transport, storage and testing than RT-qPCR specimens. Secondly, because antibodies are typically uniformly distributed in the blood, serological specimens have much less variations than nasopharyngeal viral RNA specimens and can be easily collected with minor phlebotomy discomfort to the patient. Thirdly, unlike RT-qPCR, serological tests can detect past infection because virus-specific antibodies (unlike viral RNA) can persist in the blood for several weeks/months after onset of symptoms. IgM/IgG serological tests also have some limitations, mainly related to the slow pace of the human antibody response to SARS-CoV-2. Although, several studies are still on-going, SARS-CoV-2 antibodies may not be detectable before 3 days after onset of symptoms (or at least 7 to 10 days after infection)1-3. While IgM/IgG serological tests alone may not be enough to diagnose COVID-19, they can be a valuable diagnostic tool when combined with RT-qPCR (see section below). In addition, because of their scalability, serological assays can be used in large-scale, whole-population, testing to assess the overall immune response to the virus and identify asymptomatic carriers of the virus. Indeed, 20-80% of COVID-19 cases are estimated to be asymptomatic1.