The current COVID 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, according to ICMR. RT-PCR (Reverse Transcription Polymerase Chain Reaction) tests have been used since the pandemic started. and the RT-PCR result contains the CT value.

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What is CT value?

According to the American Association for Clinical Chemistry (AACC), CT (cycle threshold) value refers to the number of cycles needed to amplify the viral RNA to a detectable level. In simple words, the CT value is a scale of measurement of the viral load in a patient. The lower the CT value, the higher the severity and vice versa. A patient is considered COVID-19 negative if the CT value is 35 in the RT-PCR test. If the CT value is below 35 in the RT-PCR test, a patient is a COVID-19 positive.

The Maharashtra government had earlier this month asked the ICMR to reduce the CT value cut-off from 35 to 24 for positivity rate under the RT-PCR test. This would cause a fall in the positivity rate. However, ICMR denied.

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Why is CT value important for COVID patients?

Apart from just determining the presence of a pathogen, the CT quantification helps to establish the pathogen burden and distinguish between what are normal and commensal levels. 

What is a safe CT value range?

The ICMR states that the globally accepted cut-off for CT value for COVID-19 ranges between 35 to 40 depending upon the instructions laid down by individual manufacturers.

It further states that "patients with a CT value of equal to or less than 35 may be considered positive, while those with a CT value greater than 35 may be considered negative."

Always remember lower CT value = Higher viral load and higher CT value = lower viral load. So a CT value of more than 35 is considered safe and anything lower falls in the 'positive' category.

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What are the limitations of RT PCR tests?

While RT PCR tests have been widely sought since the beginning of the pandemic, it has been criticised for depending on numerous factors. The values can vary depending on the method of specimen collection, source, transportation, and the time gap in contracting the infection, collection, and analysis. These tests are relatively costly the process is longer. 

How to download the results of your RT-PCR test?

  • Visit the official RT PCR website: https://covid19cc.nic.in/.
  • Key in your user ID, password, and captcha, and login into your account. 
  • Enter your mobile number and OTP. 
  • Now, you will be able to download all the reports, which are in PDF form, together.