Dear friends, there is a lot of confusion is going on regarding the CT (Cycle Threshold) value of RT- PCR for COVID-19. I have just highlighted here a few points related to CT Value. First, you must keep in your mind that there is no correlation of CT value with the clinical condition of a patient.
What is CT Value?
CT value is the Cycle thresh-hold for RT PCR testing, which helps the Virologist/Microbiologist in taking the decision of the result of test. In simple language, you can understand this as when your COVID positive sample goes inside RT PCR Instrument, the machine tries to detect Viral RNA/ genom and at the moment when it finds/amplifies the viral RNA, it gives a signal and it is called Ct Value.
ICMR (Indian Council of Medical Research) already has asked us not to correlate this value with clinical condition or transmission of virus ability of an individual. Various factors are responsible for the alteration of this value as such as Method of sample collection, Method of RNA Extraction, the timing between sample collection and processing of RT PCR, Viral load of the patient, the testing kit used for RT-PCR and also handling of the sample by a lab technician, etc.
A common conception is Low CT value is dangerous and High CT Value is safe. But it is a false conception that a person with a high viral load may have a high CT value and can spread the virus rapidly. It may be HIGH in seriously ill patients and low in asymptomatic individuals.
I have picked up the CT value of 4 different patients here which is 15.
Now, what is your interpretation? As general thinking, these all may be seriously ill, But NO, that's not the case. Two patients among these have mild symptoms and are in home quarantine; one is moderately ill with home quarantine and one is Hospitalized on Oxygen therapy.
Hope you may understand the role of CT Value.