As the number of COVID-19 cases continue to increase across the country, the Karnataka and Kerala governments are planning to procure and introduce rapid testing kits to amp up testing. However, experts advise caution while using rapid test kits, as they may be more prone to false negatives and false positives.
What are the rapid tests and what are the things that need to be kept in mind when they are used?
Rapid testing kits are serology-based tests that work by determining if there is presence of an antibody found only when a particular pathogen is present (in this case the novel coronavirus). However, since the test only measures the presence of the antibody, experts say that it cannot be used as a standard measure to confirm whether an individual is indeed positive for the virus. Results are made available within 30 minutes.
Though the two states have said the kits will be sourced from the Indian Council of Medical Research (ICMR) and have been approved for use by the National Institute of Virology in Pune, ICMR has issued clear guidelines for their use. As per the guidelines, rapid tests are not recommended for diagnosing COVID-19. ICMR stated that while a positive test result indicates there has been recent exposure to the virus, a negative result cannot be taken at face value and does not mean that an individual isn’t positive for coronavirus.
"Positive test indicates exposure to SARS-CoV-2. Negative test does not rule out COVID-19 infection," ICMR says.
When a virus enters a host, the host’s immune response is triggered. In humans, a specific antibody forms as a response to the presence of the novel coronavirus. While those who have been confirmed to have contracted COVID-19 will definitely have the presence of the antibody, it is not indicative of an active infection. Individuals who have come in contact with the virus (either via direct contact or after interacting with a positive individual) may also have antibodies against the virus in their body but may not have any symptoms.
Furthermore, carriers of the virus may not be symptomatic but could still have the virus in their body in large enough numbers to transmit the infection to another individual, but not a large enough presence to incite an immune response which produces the antibodies.
The PCR test, which is used to diagnose and confirm COVID-19, checks for the presence of the virus’ genetic material in an individual’s blood. The coronavirus has genetic material in the form of RNA rather than DNA. The PCR test amplifies the presence of any viral genetic material, thereby allowing for the identification of the virus in the individual’s sample.
Why is the test being used if it cannot detect the presence of the virus?
While the rapid tests cannot determine if there is an active infection of the coronavirus, according to a release from the Kerala government it will determine if there has been any viral infection in the recent past. However, further tests will be required to determine if there is an active infection of the novel coronavirus.
The use of the rapid tests in the community will also be able to help determine if there is any community transmission of the coronavirus disease.