Covid-19 Serological Tests: A Journey from Denial of Reality to Conclusive Insights

In response to the outbreak of COVID-19, caused by the SARS-CoV-2 virus, several tests are needed for diagnosis of acute illness, contact tracking, diagnosis of asymptomatic infections, and assessment of herd immunity. While PCR is the standard test in acute type, serological tests have been developed and used to meet diagnostic needs due to the widespread prevalence of the disease. Unlike the availability of high-throughput PCR assays, cross-reactivity is a major challenge for COVID-19 antibody test. Given that there are six other coronaviruses that infect humans, the development of highly specific serological methods to identify infected patients will be of paramount importance. Laboratory diagnostic tests play an important role in preventing the spread of infectious diseases, as evident in the case of COVID-19. Within incipient days of the release of the SARS-CoV-2 genome, PCR tests were rapidly being pioneered to diagnose patients with acute pneumonia in China and worldwide. As the disease spread, it became clear that PCR testing alone could not meet the needs of the society and shortcomings gradually appeared, such as lack of ability in retrospective contact tracing, lack of ability in detecting asymptomatic patients, and inability in assessing herd immunity. Although in several countries, serological tests are being used in contact tracking, seroepidemiological studies and planning and determining different strategies in controlling COVID-19, unfortunately, different opinions about the use and quality of serological tests are given in cyberspace which are mainly based on little information at the beginning of the production of serology kits and at the time of low prevalence of the disease. This paper is an overview of the use of different strategies to increase the sensitivity, specificity and positive predictive value of serological tests and examining the impact of various factors on these characteristics. Scientists have developed a large number of antibody assays, and many of these tests are now commercially available. Although none of these measurements have been fully validated, FDA has issued Emergency Use Authorization (EUA) for some tests while emphasizing the need for further validation. This is because the widespread use of unapproved tests could lead to policies that exacerbate rather than control the current SARS-CoV-2 epidemic.