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What is the cycle threshold (Ct) in terms of PCR

platform?

Dr. Ravi: Cycle threshold (Ct) value in terms of PCR platform is in-built into the machine.
What they actually measure is the fluorescence signal. During the test, there would be
something in which we call a “scope.” When the probe binds to our target, that is when
amplification will occur, as the signal gets boosted more, it would be captured by a detector
in the machine. The threshold is in-built in the machine, which will minus the background,
and as it passes the section threshold, it would become positive. This is how we would
evaluate, but having said that, it has to be a sigmoidal, S-curve. This is where we would
evaluate if it is positive, or not positive.

Let’s say, if the Ct value is 40, above 40 would be negative. Having said that, if the Ct value
is between two types of samples, what we usually think would be the higher load would be,
the lower Ct value, the higher viral load. The Ct value of 50 is the higher viral load which is
translated to a higher risk of transmission. As compared to someone with a Ct value of 58, it
may not be similar. 34 and above, there is no means of surviving (the virus does not survive).
That would give us an indication.

Datuk Dr. Chris: This is just for clarification, as when we changed the guidelines for patients
on discharge. Some people did not understand this part very well. It is just a fine tuning of
positive, negative results.