jack123 said:
Iv'e had enough of this BS!!!! The restrictions being imposed on us, are IMO without valid reason, next step curfews and restricting alcohol sales, then what ever other rubbish they come up with.. Cases this, cases that.. Iv'e been reading a bit today about this PCR test, in the past I have read about it was never meant for this! Now in the last few days, I'm reading from many, many people that the way they conduct the tests, they could find everybody positive if they wanted to!
I haven't read it all, because there are pages and pages of the stuff, but it's to do with the amount of cycles they are using 45? I believe.
PCR - polymerase chain reaction just amplifies a target sequence of DNA- usually 500-2000 bases (C, G, A , T) very specifically. This was developed in the late 1980s. All PCR uses short pieces of DNA called primers- short templates that match the start of each of the two strands of DNA. The DNA is heated to separate the strands. If the primer matches the target it binds and replicates an enzyme Calle Taq polymerase. Taq is heat stable so you have a cycle of denaturation, amplification and annealing.
After cycle one you have two copies of the target. Four after two, eight after three and so on.
The diagnostic is a quantitative real time PCR. In this there is also a probe sequence bound to a fluorescent dye.As
Coronaviruses are RNA not DNA viruses we convert the RNA first using another enzyme.
In each cycle, as the probe binds to the amplified sequence the dye is released and a laser detector picks up the light signal. The more target (virus) the more signal. There is usually a threshold signal set. So for example if there were a million viruses it may take 10 amplification cycles to reach the threshold (or Ct), 20 for a thousand,
30 for 10. The test is very specific and sensitive. The problem is a cut off. We use qPCR in a different way and run a max of 40’cycles. There is some doubt that positives after 40 or more cycles are viable Virus . This has been badly reported. The suggestion made is that reports to medics etc should show the Ct value as this is a good indication of not only infection but the level of virus,
Not the test is bad
The method is not new- have used qPCR since 1999,
But each set of primers and probe are designed specifically to amplify and detect an individual sequence. What you have read is at best misinterpretation and worst complete rubbish. Saying it is not a Covid test is a bit like saying Picasso is rubbish because he used paints like DaVinci
