2. What is the meaning and significance of Ct Value in an RTPCR test? Explain. (10 Marks)
आरटीपीसीआर परीक्षण में सीटी वैल्यू का अर्थ और महत्व क्या है? समझाएं।
Students are expected to write about the Ct value it’s meaning and significance in the test of RT PCR.
Among various scientific terms that the Covid-19 pandemic has made part of the public vocabulary, one is the ‘Ct value’ in RT-PCR tests for determining whether a patient is positive for Covid-19.
- According to the ICMR advisory, the Ct value of an RT-PCR reaction is the number of cycles at which fluorescence of the PCR product is detectable over and above the background signal.
- Put simply, the Ct value refers to the number of cycles after which the virus can be detected.
- According to the ICMR, a patient is considered Covid-positive if the Ct value is below 35. In other words, if the virus is detectable after 35 cycles or earlier, then the patient is considered positive.
- If the benchmark were to be lowered to 24 the value mentioned by state of Maharashtra it would mean that Ct values in the range 25-34 would not be considered positive.
- Ct value determines the detectable level of the virus in a given sample based on which it is decided if the person is COVID positive or negative.
- A benchmark of 35, therefore, means that more patients would be considered positive than we would get if the benchmark were 24.
- The ICMR has said lowering Ct threshold parameter may lead to missing several infectious persons.
- One can think of Ct value as a measure of transmission potential. So if there is more virus in my throat and nose, I will transmit it better.
- Although Ct value is inversely correlated with viral load, It does not have any bearing on the severity of the disease, experts have said.
- A patient can have a low Ct value, which means her viral load is high enough to be detected rapidly, but she may still be asymptomatic.
- The Ct value tells us about the viral load in the throat and not in the lungs.
While whether Ct value alone can determine the risks, severity and infection level in an individual still remains debatable, many clinicians, researchers consider it as one of the many parameters that hold potential in determining the dynamics of the infection and in efforts to control the transmission.