What CT value in COVID-19 RT-PCR test is; steps to calculate

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Amid a surge in COVID-19 cases, the Maharashtra government earlier this week had requested the Centre to reduce the cycle threshold (CT) value cut-off from 35 to 24 for positivity rate under the RT-PCR test. They had asked to reduce the CT value for a lesser number of patients who come under the positive category.

Days later, the Indian Council of Medical Research (ICMR) rejected the Maharashtra government's request. While replying to them, the ICMR said, "Implementing a CT value cut-off of 24 is not at all advisable, as this will lead to missing of several infectious patients and increased disease transmission. CT value threshold helps to identify whether a patient is COVID positive or not."

What is CT value and why is it necessary?

The CT value refers to the number of cycles needed to amplify the viral RNA to a detectable level, according to the American Association for Clinical Chemistry (AACC). An individual is considered COVID-19 negative, only if the CT value is 35 in the RT-PCR test. So, if the CT value is below 35 in the RT-PCR test, then the patient is coronavirus positive.

How is CT value calculated?

The measurement of CT Value represents iGenetic Diagnostics' that provides Cycle Threshold (CT) value on Reverse Transcription-Polymerase Chain Reaction (RT-PCR) test reports. Once the sample is collected from the patient, RNA is extracted and treated with a reverse transcriptase enzyme. A complementary DNA is extracted from an initial RNA. Following that, the DNA can easily be amplified by using a polymerize chain reaction to make billions of copies of a fragment.

The DNA is measured in real time by fluorescent dye signals, through which it helps to calculate the CT Value. Meanwhile, in the exponential phase, fluorescent signals data is collected which is the starting amount of the target DNA. Always remember: LOWER CT VALUE = HIGHER viral load and HIGHER CT VALUE = LOWER viral load.

Steps to download RT PCR test report:

Step 1: Visit the official RT PCR website - covid19cc.nic.in >Step 2: Enter your User ID, password and captcha correctly >Step 3: Log in to your account >Step 4: After logging in, enter your mobile number and OTP >Step 5: Within minutes, you will be able to download all the PDFs together

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