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, it has its limitations too. Serological or antibody 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 fewer variations than nasopharyngeal viral RNA specimens and can be easily collected with minor phlebotomy discomfort to the patient. Dr P Siva Kumar, Med Tech Consultant, ESI MedTek Solution in a quick conversation with Raelene Kambli explains the significance of Rapid antibody tests
What is the difference between rapid antibody tests and the RT-PCR tests?
Rapid Antibody Tests are quick to perform just with a drop of blood from a finger prick. There is no need for an experienced lab technician to draw the blood or transport the blood. Instantly, it can be applied on the device and there will be an indication within five to 15 minutes (depending on the manufacturer) whether the individual has antibody for the virus/viral protein or not. Antibody test will reveal the presence of antibodies for the virus and antibodies are formed after the infection is suppressed. It does not give an indication of the current infection. It is not a diagnostic test but a screening test that tells whether one was infected or not.
RT PCR Tests will measure the presence of Nucleic Acid (RNA or DNA) from the virus. It provides information on the current infection and will be negative once antibodies are formed. In the case of COVID-19, it is 10-20 days. Even if someone got infected with the virus and had no symptoms, after 15 odd days of the infection, RT PCR will give negative results. It takes two to three hours for doing a test.
Why is there a clamour for antibody kits?
My take and understanding is that rapid antibody testing is probably misunderstood to be a “diagnostic tool”. However, it is actually not. It is easy to perform, takes less time, can be done anywhere and does not require any equipment. The technician or individual who will perform this test doesn’t need to have so much of PPE as in the case of RT PCR.
Many say that these are relatively inexpensive as compared to RT-PCR test. Is that the only reason or are there any other scientific pieces of evidence that make antibody test a better choice?
The objective of using RDT and RT PCR is quite different and is not understood properly by the common man and probably people who communicate to the general public. RDTs are good tools. However, since the disease is new, the virus is new and things are evolving, it would take some time before we have authentic RDT tests. At present, some level of variation in specificity is understandable and should be accepted. It is a dynamic situation and things will gradually change to better.
How can antibody test be part of the epidemiology studies of COVID-19 and how can the data obtained from antibody testing help in understanding mathematical patterns of the virus spread? Can this also be useful for the serosurvey that the government has undertaken in 69 districts?
Since antibodies are tested in a wider population and in a shorter time, the data obtained will be quite significant and will suit epidemiologists to arrive at the patterns more easily.
If the decision to perform RT-PCR test is based on a criterion that the individual shows symptoms and generally not done in asymptomatic individuals, it is possible that individual who has been infected has not been tested because of the above reasons. However, as part of community screening, if the individual is tested, he/she will have the antibodies (definitely IgG) and in all likely hood, this individual will be resistant in future.