Cycle threshold (Ct) Value in a RT-PCR Test 

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• 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.