Lower cut off for RT-PCR test will lead to missing infections: ICMR to Maharashtra

The Indian Council of Medical Research (ICMR) has informed the Maharashtra government that it is not at all advisable to use a lower cycle threshold (CT) parameter in RT-PCR tests as it will lead to missing several infectious persons and increase disease transmission.

Balram Bhargava, Director General, ICMR, in a letter to Pradeep Vyas, Principal Secretary, Health and Family Welfare, Maharashtra, said: "Implementing a Ct cut off value of 24 is not at all advisable as this will lead to missing of several infectious persons and increased disease transmission."

Bhargava was replying to a letter by Vyas on the subject. He said the globally accepted cut off for CT value for Covid-19 ranges from 35-40 depending upon individual restrictions laid down by individual manufacturers.


However, the ICMR has taken inputs from different virology laboratories across the country to arrive at a single CT value cut off based on individual laboratory experiences.

The ICMR said as per uniform consensus, a single cut off of 35 with good sigmoidal real time RT-PCR curve is acceptable.

All patients with a CT value of less than or equal to 35 may be considered positive while those with more than 35 may be considered negative.

All samples of CT value of less than or equal to 35 with poor sigmoidal curve should be essentially retested, Bhargava said in the letter.