Immunodiagnostic testing in pandemic times

Actually, these are testing times in clinical diagnostic industry. Radio immunoassay and fluorescence immunoassay are age-old techniques, which are replaced by ELISA. ELISA continues to be the standard technique because of its high sensitivity, specificity, and precision but it is time-consuming, has low detection range, and presence of interfering factors. On the other hand, chemiluminescence is a fast-growing technology, which is more sensitive and specific, highly rapid, higher detection range, no interferences, and robust. Accuracy of the assay, speed of delivery, that is, less TAT (turnaround time), availability, and accessibility of testing platforms and the sample-type used are considered in selection of an assay. Though ELISA is being used in many laboratories as it is cost-effective, but automation reduces hand-on time required by staff, and possibility of errors associated with manual testing.

Nowadays, chemiluminescence systems are gaining momentum, which in turn results in a decline in ELISA tests. With stringent checks, rapid tests are also seeing a decline and gradually shifting to chemiluminescence. In current scenario, where the world is landed into this pandemic situation, and where India works toward flattening of the COVID-19 curve, availability of standardized immunodiagnostic assay is crucial. No doubt, molecular diagnostic tests help diagnose COVID-19, but antibody testing helps determine prevalence of infection and immunity. Antibody tests detect waning or past SARS-CoV-2 virus infection indirectly, by measuring the host immune response. In COVID-19 pandemic, antibody testing can be used to understand the sero-prevalence, extent of virus spread in households, communities and specific settings, and proportion of population already infected.
Chemiluminescence analyzers being automated are capable of producing thousands of tests a day, with minimal human intervention and errors. Antibody assays help determine previous exposure and potential immunity. They have utility in screening healthcare workers. Now, the ICMR has initiated convalescent plasma therapy trial, and so it is useful to identify donors for convalescent plasma therapy. Antibody screening test may also be useful in vaccine trials.

Many of the industries have come with the antibody testing kits for COVID-19. When antibody tests become widely available, results will indicate how many people had COVID-19 and recovered, including those who did not have symptoms. This aids in determining herd immunity in population. It can also help in contact tracing to assess who else is at risk of infection, understanding the virus’s epidemiology, in identifying groups at higher risk for infection, and also for research purpose. All of this data will help improve strategies to curb the COVID-19 pandemic.
Thus, antibody testing can be used as a screening tool to learn about the total number of people that have been infected, including those infections that might have been missed. These testings also can help estimate how much of the population has not yet been infected, helping public health officials plan for future healthcare needs. These testing surveys can also track how infections progress through the population, over time. By doing these testings, physicians can look at risk factors for disease like person’s age and underlying health conditions. And yes, testing surveys can determine how long antibodies last in people’s bodies following infection. And to all this, chemiluminescence helps in reducing the TAT and decrease the manual errors. But, as each coin has other side, the kinetics of antibody response, longevity of antibodies, the ability of antibodies to protect from repeat infection, the protective titer of neutralizing antibody, and the correlation of binding antibody titers to neutralization ability are not yet known.

Though, diagnostic industry has improved in many ways, but this is the actual time for it to come up with many new innovations in diagnostic technologies, and make available more and more services for the betterment of mankind in this pandemic situation.