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| COVID-19 testing |
COVID-19 Testing is a prime tool of this pandemic situation by which the rate of infection may be control as well as the chance of recovery may increase if it is done at the primary level of infection. That’s why World Health Organisation (WHO) always recommends to increase the Testing capacity in a country to fight against COVID-19. India now conduct near about one million testing per day.
One having COVID-19 symptoms like fever, dry cough, tiredness, aches and pains, sore throat, loss of taste or smell, rash on skin, difficulty breathing or shortness of breath and chest pain or coming in direct contact with COVID positive pateient, should do testing.
Here I have discussed that how the COVID-19 test is done?
Type of Test
There are four types of diagonastic tests are being used in India.
1. RT-PCR test
2. Rapid Antibody tests
3. Rapid Antigen tests
4. TruNat Tests
1. RT-PCR test
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| RT-PCR |
RT-PCR is is the most accurate method to dected the pathogen that causes COVID-19. We can informed about the presence of SARS-CoV-2 viruses by this test which indicate a current infection. It requires nasal and throat swabs to detect the virus’s RNA. The test is much expensive and time consuming process. Though the duration of this testing process is around 6 to 8 hours, result may take up to a day to arrive.
2. Rapid Antibody test
It is basically a type of blood test. Unlike RT-PCR, rapid antibody test requires just a drop of blood sample from the finger to determine the presence of antibodies developed against SARS-CoV-2 virus. The sample is examined for two types of antibodies — IgM which appear early in an infection and IgG, more likely to show up later. The test is inexpensive and fast that can give result in 20 to 30 minutes. But it gives confirmation only about the past infection. It can’t say anything about current infection as 10 to 14 days would be required to develop antibodies.
3. Rapid Antigen test
The test detect the antigens of virus rather than antibody. Like RT-PCR, nasal swab are collected and test for antigens of the SARS-CoV-2 virus. It is a point-of-care test, performing outside the conventional laboratory. This is also a low cost test and give diagnostic results quickly, within 30 minutes. But this test may gives false negative result. That’s why those who test negative should be tested also by RT-PCR method to rule out infection.
4. TruNat test
This test generally used for detecting tuberculosis and HIV. TruNat is a small, portable, chip-based kit, works on the same principle as RT-PCR. Here samples are collected from nasal or oral swabs and examined by the kit using RdRp enzyme to detect the virus. Though the kit produces faster results within 60 minutes, the cost of the test is not cheap.
However, the majority of the tests being conducted in India as well as worldwide are RT-PCR. So, now I am going to explain about the procedure of RT-PCR test.
A Reverse Transcription Polymerase Chain Reaction (RT-PCR) test is basically Biotechnology based morden laboratory technique by which viral genome is to be detected.
SARS-CoV-2 is a type of RNA virus. The coding of the viral genome have been sequenced already by scientist. If this genomic sequence will detect in the sample that means virus is present in the sample, the result gives positive about this virus.
Sample collection : At first samples are obtained in the form of nasopharyngeal swab from nose and throat swab from mouth by the healthcare professionals in the health centers. Then the Samples are brought to laboratory for diagonosis.
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| COVID-19 testing Sample Collection |
RNA Extraction : For RT-PCR, RNA Extraction must be carried out at first. In this process RNAs are isolated from the collected sample using guanidinium thiocyanate-phenol-chloroform solution. The extracted RNA solution is a mixture of patient’s own RNA along with the viruses RNA, if present.
Reverse Transcription : The extract RNAs are converted into complementary DNAs (cDNA) by reverse transcriptase enzyme.
Real-time PCR (qPCR) : The whole RT-PCR process is conducted in automated Kit. Here, the complementary DNAs are amplified into billions of new identical copies by repeating PCR cycles. As the kits have pre-installed Marker Lebels, cDNA of the virus if present, is attached with that markers and release a fluorescent dye. The level of fluorescence which is measured by the machine’s computer in real time on the screen, give confirmation about the presence of COVID-19 viruses in the sample and it marks as COVID-19 positive.