Syllabus Section: Health Issues

Why in News?

  • Maharashtra government sent requestto the Indian Council of Medical Research (ICMR) and sought clarity whether it was advisable to treat a person as Covid-negative if the Ct value is more than 24 and the person is asymptomatic.


  • Short for cycle threshold, Ct is a value that emerges during RT-PCR tests, the gold standard for detection of the SARS-CoV-2 coronavirus.
  • Simply put, Ct value refers to the number of cycles after which the virus can be detected. 
  • Ct value does not have any bearing on the severity of the disease.
  • In an RT-PCR test, RNA is extracted from the swab collected from the patient. It is then converted into DNA, which is then amplified. 
  • Amplification refers to 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 virus.
  • Amplification takes place through a series of cycles — one copy becomes two, two becomes four, and so on — and it is after multiple cycles that a detectable amount of virus is produced.
  • 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 fewer cycles.
  • Globally, the accepted cut-off for Ct value for Covid-19 ranges between 35 and 40, depending on instructions from the respective manufacturers of testing equipment

ICMR Response:

  • ICMR informed the Maharashtra government that it was not advisable to use a lower cycle threshold parameter as it would lead to missing several infectious persons and increase disease transmission

Source: Indian Express

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