Ct value for RT-PCR tests ‘not advisable’, ‘flawed’: ICMR to Karnataka

The Ct value in RT-PCR tests indicates the viral load of Covid-positive patients.

Published: 03rd August 2020 05:39 AM  |   Last Updated: 03rd August 2020 05:39 AM   |  A+A-

A healthcare worker wearing a PPE kit takes a sample of a woman for COVID-19 test at a residential area. (Photo | PTI)

A healthcare worker wearing a PPE kit takes a sample of a woman for COVID-19 test at a residential area. (Photo | PTI)

By Express News Service

BENGALURU:  The Indian Council of Medical Research (ICMR) has said “it is not advisable” to attach the Cycle Threshold value (or ‘Ct value’) to Reverse Transcription Polymerase Chain Reaction (RT-PCR) test results of Covid-19 patients, as requested by the state to help improve triaging of Covid-19 patients in moving them quickly to hospitals with appropriate bed and medical equipment facility as per their viral load and case severity.

ICMR Director-General Prof Balram Bhargava, responding to Karnataka Chief Secretary T M Vijay Bhaskar’s letter dated July 25, has stated in a letter that the issue of adding such a value to each test report “is not advisable and is scientifically flawed”.

The Chief Secretary had written to ICMR with the request following The New Indian Express article dated July 16, based on experts’ opinions stressing on the importance of attaching the Ct value to test reports to make bed allocation more efficient to ensure a better patient recovery rate.

The Ct value in RT-PCR tests indicates the viral load of Covid-positive patients. Experts said that to reduce the time taken to provide appropriate treatment to Covid 19 patients, especially those under high risk, authorities would direct laboratories to attach Ct values to enable health officials to understand the urgency or the severity of the case. For that, ICMR’s clearance was required.

However, ICMR chief Prof Bhargava said, “There are no reliable studies to definitively prove a direct correlation between disease severity /infectiousness and Ct values. Viral load also has no role in patient management … Samples from asymptomatic and mild cases show Ct values similar to those who develop severe disease.” He has explained to the Chief Secretary that patients in early symptomatic stage “may show a high Ct value which may subsequently change.

In such cases, high Ct values will give a false sense of security. Severity of Covid disease largely depends on a host of factors besides the viral load. Some patients with low viral load may suffer from very severe disease due to triggering of the immunological responses.

Hence, again high Ct value may give a false sense of security.” He pointed out that Ct values differ from one diagnostic kit to the other and compatibility of Ct values among different kits is a challenge as labs across the country are using a mixed basket of kits.

Ct values also depend on how the sample has been collected. “A poorly-collected sample may reflect inappropriate Ct values. Besides, Ct values are also determined by technical competence of the person performing the test, calibration of equipment and pipettes and analytical skills of the interpreters,” he said.
“Moreover, the RT-PCR test presently being conducted is qualitative in nature. Ct values may give only a rough estimate of viral load. In view of the above, it is not recommended to rely on Ct values for Covid-19 patient management,” Prof Bhargava has stressed.

For reporting Rapid Antigen Test (RAT) results through the RT-PCR app, ICMR will be working with the National information Centre (NlC) to make the whole process user-friendly and less time-consuming, Prof Bhargava has informed Chief Secretary T M Vijay Bhaskar.


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