Testing is an indispensable part of the strategy to rein in Covid-19. Since the first cases were reported in India, more than a year back, testing capacity and capabilities have been widely augmented in India with steps being routinely taken to increase testing coverage and improve the process. The latest innovation is the saline gargle solution for the RT-PCR test that has now received approval from the Indian Council of Medical Research (ICMR), which comes on the heels of a home test kit.
RT-PCR: The best is also the costliest
It is called the ‘gold standard’ for Covid-19 tests because of the high level of accuracy it provides. Sars-CoV-2, or novel coronavirus, the virus that causes the Covid-19 infection, is an RNA virus and it is in the detection of RNA viruses that the RT-PCR test, devised some time in the 1980s, is the benchmark despite being time consuming and relatively costly.
As the name suggests, the test has two parts; the RT stands for ‘reverse transcription’ and involves the conversion of the RNA sample into DNA. PCR stands for ‘polymerase chain reaction’ and is the part of the test that measures the amount of the specific RNA.
So, what lab technicians do is use an enzyme to convert the virus’s RNA into DNA, which allows a single DNA molecule to be amplified exponentially (millions of times). This is the reason for the accuracy level of the test as virus particles in even single digits can be detected from oral and nasal swab samples.
The test also involves the use of primers, which are DNA bits that are intended to bind only with the specific Sars-CoV-2 DNA obtained via reverse transcription. Among the elements for the test is also a fluorescent dye, which acts as the probe and marks out the presence of the virus after being processed through the PCR machine.
Among the bottlenecks reported with the RT-PCR test is the requirement of the collection of oral and nasal swabs and transporting it to the lab. But the saline gargle solution provided by scientists at the National Environmental Engineering Research Institute (NEERI) promises to not only make sample collection easier but also reduce the time and cost of the RT-PCR test.
In the early days of the pandemic, an RT-PCR test could cost up to Rs 4,500, but the prices have since been reduced across the country.
Simple, quick and cheap: Rapid Antigen Test
The USP of this test is speed even as accuracy can prove to be an issue. Specifically for detecting Covid-19, antigen in RAT test refers to the novel coronovirus’s spike protein, which it uses to invade human cells. Antigen essentially is any foreign substance that can elicit an immune reaction from the human body, which begins producing antibodies to fight the invader.
The antigen test for Covid-19 seeks out Sars-CoV-2’s spike protein. The sample for this test is a nose swab that is immersed in a solution to deactivate the virus. A few drops of this solution are then introduced to a test strip that contains artificial Covid-19 antibodies. If the sample is positive for coronavirus, coloured lines will show up on the paper strip in 15-20 minutes.
As is evident, RAT does not involve amplification of the genetic material that is being tested and, hence, if a swab fails to pick up adequate amounts of the antigen, the test will return a negative result even when infection is present. This is called a false negative result. However, RAT still has its uses because if a person showing symptoms tests positive via this method, the result can be taken to be accurate. This saves both time and money as compared with the RT-PCR test given that RAT costs just a fraction of what RT-PCR tests cost.
But it has been recommended that a person who is exhibiting symptoms but has a negative RAT report should get an RT-PCR test done to confirm the result.
A Made-In-India Test Kit: TrueNat
To begin with, the TrueNat test is also an RT-PCR based test. It was originally developed to detect tuberculosis and, amid the Covid-19 pandemic, was initially used to only screen for the novel coronavirus. But the test was subsequently tweaked to recognise an enzyme found in the Sars-CoV-2 RNA. The big advantage is the TrueNat test kit, which is chip-based and battery-operated, which means it can be deployed in far-flung areas which may not have access to the more common RT-PCR test or RAT.
This test also needs an oral or nasal swab but returns the result in about 30 minutes. It is also cheaper than the lab RT-PCR test. The TrueNat test being used in India was developed by Goa-based startup Molbio Diagnostics.
It Can Reveal If Covid Had Struck: Antibody Test
Also known as the serological test, this one does not check for an active infection but can tell whether a person had contracted, and recovered from, Covid-19. So, instead of a nasal or oral swab, what is collected for the antibody test is a blood sample as antibodies to a pathogen are found to be abundant in blood. Two specific antibodies are sought out: IgM antibodies, which develops early on in an infection, and IgG antibodies, which are mostly found after someone has recovered from the infection.
For this test, the blood sample is added to a cartridge that contains SARS-CoV-2 proteins. If antibodies to Covid-19 infection are present in the sample, they will bind to the virus proteins, returning a positive test. Antibody tests can cost under Rs 1,000 in India.