A laboratory staff wearing Personal Protective Equipments (PPE) conducts a procedure from samples collected for Covid-19 coronavirus testing.
PCR stands for “polymerase chain reaction.” As Rezeq explained, it’s an “amplification testing methodology.”
“If, in theory, you have one single viral particle in the patient's specimen, that single viral particle in this polymerase chain reaction technique is amplified into tens of thousands and hundreds of thousands of particles for it to be detected,” he said.
The reaction goes in cycles — one molecule becomes two, two becomes four, and so on, for a predetermined number of iterations. The limit of those iterations is called the cycle threshold, and it’s set by the manufacturer of the test itself (and approved by the FDA).
So, for example, if the cycle threshold is 37, that means if you have no positive identification of a virus after 37 iterations, the test is negative. The fewer cycles needed to detect a virus, the higher the viral load in the patient.
You can also grow a specimen in a culture, but that takes far longer than a PCR test (on the order of weeks, instead of minutes). less