PCR Tests. What are they and how do they work?
This explanation will be very, very simplified, but I hope it can give you a grasp on what the PCR test can do, what it can’t do, and how it has been misused in this pandemic.
The PCR test.
Here are two images of the DNA which is in nearly every cell in your body. The left image is a fairly complex model whereas the other image is very simplified. The DNA is like a ladder – two side bars with rungs in between. It’s a bit like a zip.
The PCR test pulls the zip apart to produce two halves of the zip, each with half rungs. The PCR test then picks up matching half rungs from the oceans of ‘spare parts’ it’s floating in and this makes two copies of the original DNA.
OK. Don’t worry about the names – just look at the picture.
The original twisted DNA (helix) is coming in from the right. The green disc untwists it. The blue ‘fork’ opens the zip. We now have two halves of the helix.
The two halves then pick up matching bits from the surroundings and on the left we now have two copies of the original. (I know the upper and lower parts look different. That’s because they’ve got to be rebuilt in opposite directions, but for the purpose of this post, you don’t need to know about that).
The original DNA strand has produced two copies.
This is Cycle number 1. (Ct 1)
The second cycle copies the two strands and makes four.
The PCR then repeats this process, each cycle doubling the number of copies of the DNA,
So, starting with just one sample of virus DNA the cycles produce copies as follows.
After 10 cycles 1,024 copies
After 20 cycles 1,048,576 copies (over a million)
After 30 cycles 1,073,741,824 copies (over a billion)
After 40 cycles 1,099,511,627,776 copies (over a trillion)
Why does the PCR test keep on doubling the copies?
The Coronavirus, SARS-Cov-2, is very, very, small.
Ten thousand of them side by side would measure about one millimetre. So, they are very difficult to see. We need to use special microscopes, electron scanning microscopes.
In order to carry out testing, we need large numbers of the virus. This is where the PCR process comes in. Just to give you an idea, special markers are added which glow a measurable amount when a certain number is reached. (More or less – very oversimplified)
As you can see, if PCR is used to tell if a person is infected, the result, whether positive or negative, depends on the number of cycles.
For example, fewer than 20 cycles will almost always produce a negative result, whereas 40 cycles and above will almost always produce a positive result.
The test is used to find out if the person is infected.
The problem is that the PCR test does NOT diagnose an infection. It just finds out if the virus is present in the sample.
According to a study carried out by Jaafar et al. 2020:
“If someone is tested as positive when a threshold of 35 cycles or higher is used (as is the rule in most laboratories in Europe and the US), the probability that said person is infected is less than 3 percent, and the probability that the said result is a false positive is 97%”.
YES, out of every 100 positive results, 97 will be FALSE – no infection.
According to some reports, laboratories in the UK use up to 45 cycles which means that ALL the results will be positive.
The worry here is that the authorities can produce any result they want by controlling the number of cycles used. And the number of cycles is not disclosed.
Also, when you have a PCR test, you have no way of finding out how many cycles were used. Not even your doctor is given that information.
This test was invented by Kary Mullis in the 1980s, and he said that it should NOT be used to diagnose an infection – that it was an analytic tool, not a diagnostic one.
The way the test should be conducted was laid down by the World Health Organisation (WHO) based on the Corman-Drosten paper. This paper has been torn apart by many experts because of its many flaws and its use of the 2003 SARS-CoV as a control because there was no actual virus available at the time.
“We aimed to develop and deploy robust diagnostic methodology for use in public health laboratory settings without having virus material available.” (my underline.)
Some comments from official documents and studies
The following from an NHS publication (source below) suggests that a positive PCR test is a confirmed Covid-19 infection whereas a patient who has been diagnosed by X-ray and a doctor’s assessment is only a suspected infection, i.e. not confirmed. This in spite of the fact that the PCR test can give up to 97% false positives, and that
“… a confirmed COVID-19 patient is any patient admitted to the trust who has recently (ie in the last 14 days) tested positive for COVID-19 following a polymerase chain reaction (PCR) test.”
“Patients who have been diagnosed via X-ray and assessment rather than a positive test should be counted as suspected (and not confirmed) COVID-19 patients.”
Also, from Surkova et al. (2020), a test should be sought after an assessment has been made by a medical professional that the person probably has the infection.
“Any diagnostic test result should be interpreted in the context of the pre-test probability of disease. For COVID-19, the pre-test probability assessment includes symptoms, previous medical history of COVID-19 or presence of antibodies, any potential exposure to COVID-19, and likelihood of an alternative diagnosis.”