RT PCR
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Context
- India reported 18,819 new Covid-19 cases and 39 deaths in the last 24 hours. With rising Covid-19 cases in India, states have been asked to screen 2% of the international passengers coming to India at random and send all positive samples for genome sequencing.
RT-PCR
- The real-time polymerase chain reaction (RT-PCR) test is the most commonly used one for Covid-19. It is primarily based on PCR, a process that repeatedly copies and amplifies the specific genetic fragments of the virus, ensuring that there is enough of a sample to conduct the analysis.
- The RT-PCR test starts with a simple swab taken from inside a person’s throat or nose. Coronaviruses have RNA or ribonucleic acid as their genetic material. However, swabs from patients yield only a tiny quantity of RNA, which is not adequate for the testing process.
- To overcome this problem, the RNA — a single-strand molecule — is converted into a two-strand DNA using an enzyme. This is known as reverse transcription.
- Researchers select specific areas in the genome that do not mutate rapidly as the virus evolves, and create copies of these using the PCR process.
- The next step is the use of primers. These are small pieces of DNA designed only to bind to the selected DNA sequence of the SARS-CoV-2’s viral genome. Along with primers, the process uses a fluorescent dye, which acts as the probe.
- The patient sample, primer and probe are together left in the PCR machine for the binding process to take place. A fluorescent signal marks the presence of the virus.
- The time duration for the testing process is around four to eight hours.
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