- Types of test for COVID-19 – tests for antibodies, tests for the virus
- Antibody test shows accurate results only after a week of being infected
- In India, RT-PCR test is being followed for the diagnosis of COVID-19
New Delhi: Test, isolate and trace is what the World Health Organisation’s advice on strategy to deal with the coronavirus pandemic. As India scales up its testing even as it tries to slow down the rate of transmission with the extension of the lockdown till May 3, India has updated its testing guidelines. On April 9, the Indian Council of Medical Research (ICMR), the nodal body for the fight against COVID-19, updated the coronavirus testing strategy for India for the fourth time and noted that individuals present in the hotspots and showing symptoms like fever, cough, sore throat, and runny nose, will be tested. Initially, ICMR resorted to testing individuals returning from foreign countries and showing symptoms.
Also, earlier RT-PCR (Reverse transcription-polymerase chain reaction) test was done. Later, ICMR introduced antibody test for COVID-19 and on April 13, ICMR issued an advisory on the feasibility of using pooled samples for molecular testing of COVID-19.
Given the different kinds of tests for COVID-19, NDTV spoke to experts to learn more about these tests and their effectiveness.
Why Are Tests Crucial For Combating COVID-19?
Before we move to understanding these tests for COVID-19, let’s quickly understand why testing is required. Time and again, experts have mentioned that testing is the only way to know the accurate status of the pandemic. Testing is essential to see who, why, where, and how many are infected by the coronavirus.
In a media briefing, Dr Tedros Adhanom, Director general of the World Health Organisation has also emphasised on testing and said,
We have a simple message for all countries: test, test, test. Test every suspected case. The most effective way to prevent infections and save lives is breaking the chains of transmission. And to do that, you must test and isolate.
In the case of lack of testing, if two people get infected and they have not been diagnosed and quarantined then they can spread the virus to potentially 800 people. Whereas, in case of adequate testing, if two people get infected, and identified then they can be in quarantine; and so the spread of infection curtailed as these two can potentially infect a maximum five people, as compared to 800 in the earlier scenario.
Types Of Covid-19 Tests
There are two types of tests for COVID-19 – tests for antibodies and tests directly for the virus – RT-PCR test and NAT test.
Antibody Test For COVID-19
Antibody tests are similar to a blood test, using a few drops of blood to determine whether the human body has antibodies for coronavirus. Antibodies are proteins produced by a human body and used by the immune system to identify and neutralise foreign objects such as bacteria and viruses. Though antibody test costs Rs. 500 and gives result in 20-30 minutes, but testing for anti-body can be misleading in the first week of infection.
From the day of contracting the virus to day 7, an individual will start showing the symptoms of COVID-19 and may start infecting others as well but even after repetitive tests, there is a possibility antibody test will give a false negative. The reason being, antibodies take eight days to develop and actually appear. This means, antibody test will give accurate results from the eighth day of being infected.
Talking about the relevance of antibody test and at which stage it should be done, Gagandeep Kang, Executive Director at Translational Health Science and Technology Institute (THSTI) said,
The antibody test looks really easy to do but there is a problem with a test, not just in that they become positive only in the second week of illness but the validation of these tests are also much harder than validating molecular tests like PCR and NAT. Since antibody tests have not been around for a very long time, there is a lot of testing that needs to be done before we create an appropriate use case for them anytime early in illness. In late illness or looking to see who can safely go back to work, definitely these antiboDY tests have value but in early illness, they will provide you with false results.
NAT And RT-PCR Tests For COVID-19
For testing the virus, there are two kinds of tests available – NAT (Nucleic Acid Test) and RT-PCR (Reverse transcription-polymerase chain reaction) test. Both tests require a nasal and throat swab. While NAT costs Rs. 2,800 without duty and takes about an hour, RT-PCR costs Rs. 4,500 and requires five to six hours to test the samples thoroughly.
Both NAT and RT-PCR test lookout for virus hence they give positive results from day one. Though NAT test has been approved by FDA (Food and Drug Administration), currently, in India, RT-PCR is being followed for the diagnosis of COVID-19.
Also Read: Why Is A Lockdown Important?
Elaborating on NAT and RT-PCR test, Dr Navin Dang, founder of Dang’s Lab said,
The need of the hour is the PCR test because even a single patient who skips the test at an early stage is capable of infecting a large number of patients. But, if we immediately test, quarantine, the number of contacts which he/she would have infected will be much lower. At the moment, when the disease is in an early stage, when the infection is in an early stage, the need is only PCR test.
Echoing the same, Ms Kang said,
If you look at what needs to be done in early infection, very clearly we need to go for PCR or NAT test if we can get it. The problem right now with NAT test is, it’s not available. And we should be putting in efforts to making sure that we can get the test.
Complexity Of COVID-19 Tests
Of the three tests, RT-PCR is not only expensive but requires highly qualified technicians and the entire process – from collecting the sample to delivery of report – takes a day. Talking about the complexity of three tests, Ms Kang said,
Doing PCR does require a fair degree of complexity and training because you have to be very careful not to cause contamination of the area that you are working in. NAT tests are easier to do and antibody test is the easiest of all. In fact, in many parts of the world, people are thinking of doing it as an at-home test which can be shipped to houses so you can test yourself at home, similar to doing a diabetes test.
Should India Stock Up Antibody Tests?
Considering the fact that antibody tests give accurate results only after a week of getting infected, in its latest testing strategy dated April 9, ICMR has made it clear that individuals living in hotspots and showing influenza-like illness (ILI) symptoms will undergo RT-PCR test. Only after seven days of illness, anti-body test will be done.
Since India is following RT-PCR, should a country stock up antibody tests? Answering the same, Ms Kang said,
Absolutely, zero epidemiology is one of the key tools of public health. Understanding what proportion of the population has been infected allows you to direct public health efforts accordingly. If you look at what is happening now, there is more and more evidence that people can spread infection when they are asymptomatic or pre-symptomatic. So, we will never know who has had contacts with whom and the only way to detect this at a population level is to look for the presence of a signature in the blood which is antibodies demonstrating that you have been previously exposed to the virus.
What Is Pooled Testing?
A pooled testing algorithm involves the RT-PCR screening of a pool comprising multiple individual patient samples. If a pool turns out to be negative, all individual samples involved in that particular pool are regarded as negatives. On the other hand, if a pool tests positive, pool de-convolution – individual testing of samples is done.
Why Is Pool Testing Done?
The pooled strategy testing is being adopted in other countries like Germany. On April 13, to increase the number of tests in India, ICMR also issued an advisory on the feasibility of using pooled samples for molecular testing of COVID-19. In its advisory, ICMR has suggested the pooling of only five samples.
Talking about the effectiveness of pooled testing, Ms Kang said,
Pooling is very useful when you have a low prevalence of infection in a population. Once you get up to a considerable part of the population potentially infected then pooling loses its value because you will have to go back to the individual samples if your pool turns out positive. To start with, yes, absolutely, pooling is a cost-efficient way of testing a lot of samples. Later in the course of epidemic, that might not be the case.
In its advisory, ICMR has recommended the use of pooled testing only in areas with a low prevalence of COVID-19 (areas detecting up to 2 per cent positive samples). In areas with the positivity of 2-5 per cent, pooling of samples may be considered only in community survey or surveillance among asymptomatic individuals. The pooling of samples is not recommended in areas or AMONG A population with positivity rates of over 5 per cent.
According to the ICMR’s SARS-CoV-2 testing update, over 8 lakh (8,30,201) samples have been tested as on April 30, 2020, 9 AM. To ramp up the testing, India is procuring test kits from different countries like China, South Korea. On April 16, China dispatched 6.5 lakh coronavirus medical kits to India to help in quickly IN identifying and isolating COVID-19 patients. The shipment, part of a total order of around 20 lakh kits to be delivered over 15 days, includes Rapid Antibody Test kits – a blood-based test that is more accurate and allows for quicker detection of the novel coronavirus.
Nearly 3 Lakh Rapid Antibody Tests have just been airlifted by @airindiain from #Guangzhou | Supplies are headed to Rajasthan and Tamil Nadu. Great work on ground by our team at @cgiguangzhou pic.twitter.com/uF5JxpKsve
— Vikram Misri (@VikramMisri) April 18, 2020
On April 18, nearly 3 lakh rapid antibody test kits were airlifted to transport them to Rajasthan and Tamil Nadu.