12-05-2021 | 15:05 PM
Cycle threshold (Ct) Value in a RT-PCR Test
• According to the ICMR, the current positivity criteria is based on the cycle threshold (CT), which is a measure of how soon after an RT-PCR test, the SARS-CoV-2 is detected in a sample.
• The ICMR documents mention different Ct Values. Also, there are divergent views among the National Centre for Disease Control and also among Niti Aayog.
About Ct value:
• Short for cycle threshold, Ct is a value that emerges during RT-PCR tests.
• 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.
• 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 fewer cycles.
• It has been found that the time since the onset of symptoms has a stronger relationship with Ct values as compared to the severity of the disease.
Note: Globally, the accepted Ct value is between 35 and 40.
