What are coronavirus antibody tests, and can they end the lockdown?
Two kinds of diagnostic tests are being currently used in India - RT-PCR test and rapid antibodies test. Here's everything you need to know about antibody testing in India.
As the world is reeling under the COVID-19 pandemic, medical terminologies like rapid antibodies test, RT-PCR test, hotspots and containment zones have come into focus.
Dr Arvind Kumar, noted lung surgeon at the Sir Ganga Ram Hospital in Delhi, said the key to fighting the COVID-19 battle is "testing, testing and testing" and then "quarantining and treating".
"The more number of people we screen, the greater our chance of winning this fight against COVID-19. The number of tests have to be significantly increased," he said.
Two kinds of diagnostic tests are being currently used in India -- RT-PCR test and rapid antibodies test, as per the global health norms.
WHAT IS AN ANTIBODY TEST?
Unlike tests to diagnose diseases, antibody tests show who has been infected and recovered.
The human body makes antibodies in response to many illnesses and infections, including other coronaviruses. New blood tests are being developed to identify antibodies unique to SARS-CoV-2, the official name of the new coronavirus.
The tests look for two kinds of antibodies: immunoglobulin M (IgM) and G (IgG). The body quickly produces IgM antibodies for its initial attack against infections. It makes IgG antibodies more slowly and retains them longer; IgG antibodies suggest possible immunity.
A reverse transcription polymerase chain reaction (RT-PCR) test is a laboratory technique combining reverse transcription of RNA into DNA that detects the virus while the antibody tests, which use blood, detect the body's response to the virus, experts said.
"In RT-PCR, it is tested if the virus is present or not. A sample is taken from the respiratory tract of a person, throat swab or a sample from thenaseopharyngal region and then rested. The results take about 12-24 hours," said Dr Kumar noted.
Kumar said RT-PCR tests take time and are a costly affair because of its elaborate kit.
"On the other hand, the rapid antibodies test are less expensive and the results can come in 20-30 minutes. It essentially tests if the antibodies in response the coronavirus infection has been generated or not," he said.
These tests are generally used in hotspots where the infection is found concentrated in a given area. A hotspot is a zone from where a large number of COVID-19 cases are reported.
ARE RAPID TESTS REALLY BETTER TESTS?
Some companies are developing finger-prick tests that get results in minutes. Others are developing far more accurate tests called enzyme-linked immunosorbent assays (ELISA) that require sending blood samples to a lab for analysis.
"I would argue that in the present circumstance, sensitivity, specificity and accuracy are more important than convenience," said Dr. James Zehnder, director of clinical pathology at Stanford Medicine in California.
"In rapid antibodies test, the result will be positive only if the antibodies have been generated. So, even if a person is infected but the antibodies are not generated, the result will come negative," Kumar said.
In many cases, it has happened in the past that a person tested negative earlier but after a few days when he or she reached another country, the test came out positive there.
This same person would have come out positive had the RT-PCR test been conducted, but the issue of feasibility of its use.
ARE TESTS AVAILABLE TO EVERYONE IN INDIA?
The Supreme Court on Monday modified its April 8 order that asked private labs to conduct free COVID-19 tests and said the benefit will be available only to "economically weaker sections" who are covered under a government scheme such as Ayushman Bharat.
The apex court said it never intended to make testing free for those who can afford to pay.
It had on April 8 directed that private labs, which were allowed to charge Rs 4,500 for it, would not charge for the tests observing that they need to be philanthropic in the hour of national crisis.
A spokesperson of the Thyrocare labs, one of the laboratories authorised by the government to do testing, said, testing has to be done judiciously as there are less number of kits in India.
It is not yet clear how many tests will be needed - but that number could run into the hundreds of millions - or when supplies will be adequate.
HOW CAN ANTIBODY TESTS HELP END LOCKDOWNS?
Antibody tests can help calculate what portion of the population has already been infected, as well as whether infections were mild or severe.
Governments and companies could use antibody tests to determine who would most likely be safe to return to work and public interactions, and whether it is safe to lift stay-at-home orders all at once in some regions or in stages based on infection risk.
People with negative antibody tests or very low antibody levels would likely have higher risk of infection than people with high antibody levels.
India needs to "significantly ramp up" the number of tests done across the country to trace COVID-19 infection if the virus is to be contained in time, experts said.
Data obtained from the Indian Council of Medical Research (ICMR) said, till April 14, the number of samples tested stood at 2,44,893, an increase of 27,339 from the corresponding figure till the previous day (2,17,554).
Experts feel the figures are modest for a count of the size of 1.3 billion and "much more number of tests" are needed to combat COVID-19 outbreak in the country.
Dr Ravi Shekhar Jha, Senior Consultant and Head of the Department of Pulmonology at Fortis Escorts, Faridabad, said India is going in the right direction but it is not enough.
"Given the massive size of our population, the number of tests needs to be ramped up and should be conducted more rigorously. We need to do effective contact tracing and test them so that those people in turn do not infect others," he told PTI.
"The rise in number of cases happening is also because in the last few weeks during the lockdown, people who came in contact with affected people were traced and tested. This has to be increased manifold if we have to contain coronavirus in time, otherwise it will be a difficult affair," Jha said.
Dr Sandeep Budhiraja, Group Medical Director at Max Healthcare, said it has been decided to conduct coronavirus tests on "all our workforce and patients across the country".
"Priority will be to test our admitted patients and new patients being brought in. And, the front-line healthcare workers," he said.
India is doing lot of tests, but it is not enough compared to what the US and Singapore and other countries are doing, he said, adding, "much more testing needs to be done".
Another expert from a leading private hospital here, who did not wish to be named, said, "The volume of tests conducted need to be ramped up significantly to capitalise on the gains from the lockdown".
DO ANTIBODIES TO THE NEW CORONAVIRUS CONFER IMMUNITY
While antibodies to many infectious diseases typically confer some level of immunity, whether that is the case with this unique coronavirus is not yet known.
And how strong immunity might be, or how long it might last in people previously infected, is not clear. With some diseases like measles the immunity can be lifelong. With others, immunity can wane over time.
How well these tests work depends on several factors, including the time from the onset of illness, the concentration of virus in the specimen, the quality of the specimen collected from a person and how it is processed, and the precise formulation of the reagents in the test kits, experts said.
Additionally, false positive results -- that is, a test showing that a person is infected when they are not -- could occur if the antibodies on the test strip also recognise antigens of viruses other than COVID-19, such as from human coronaviruses that causes the common cold, they said.