Question

Q. Which of the following terms correctly expands the ‘CT value’ of RT-PCR tests, commonly used for detection of CoVID-19?

• A. Coronavirus Transmission
• B. CoVID-19 Transcription Rate
• C. Cycle Threshold
• D. Cycle Termination

Answer 1

The correct option is C Cycle Threshold

Explanation:

• CT value is the short form of cycle threshold. It emerges during RT-PCR tests, the accepted standard for detection of the SARS-CoV-2 coronavirus. In an RT-PCR test, the RNA is extracted from the sample swab collected from the patient which is then converted into DNA and amplified. Amplification is the process of creating multiple copies of the genetic material — in this case, DNA. This improves the ability of the test to detect the presence of the virus. Amplification takes place through a series of cycles — one copy becomes two, two becomes four, and so on — and after multiple cycles, a detectable amount of virus is produced.
• As per the ICMR advisory, the Ct value of an RT-PCR is the number of cycles at which fluorescence of the PCR product is detectable over and above the background signal. It means the Ct value refers to the number of cycles after which the virus can be detected. If a higher number of cycles is required, it implies that the virus went undetected when the number of cycles was lower. The lower the Ct value, the higher the viral load — because the virus has been spotted after a lesser number of cycles.