First, a sample of the person's nose and throat secretions is collected using a cotton swab. This sample contains any viruses that may be present, such as the SARS-CoV-2 virus.

Next, the RNA in the sample is extracted and treated with an enzyme called reverse transcriptase, which converts the RNA into complementary DNA (cDNA). This step is called reverse transcription.

Then, the cDNA is mixed with other reagents, including another enzyme called DNA polymerase and small pieces of DNA called primers that are specific to the SARS-CoV-2 virus. This mixture is heated and cooled in a machine called a thermal cycler, which causes the DNA polymerase to make many copies of the cDNA. This step is called polymerase chain reaction (PCR).

Finally, the PCR product is measured using a technique called gel electrophoresis, which separates the DNA fragments based on their size. If the SARS-CoV-2 virus is present in the sample, a specific fragment of cDNA that is unique to the virus will be detected. This allows the laboratory to confirm the presence of the virus in the sample.

Overall, RT-PCR is a powerful technique that allows scientists to detect and measure small amounts of RNA, such as the RNA of the SARS-CoV-2 virus, with high sensitivity and specificity.