Can you generate a positive result for COVID-19 from an RT-PCR test?

CLAIMS:

    1. A high number of amplification cycles used in an RT-PCR test will lead to a positive diagnosis of COVID-19
    2. Kary Mullis, inventor of the PCR technique, said that the RT-PCR “can not be used to diagnose infectious diseases at all”
    3. Kary Mullis was opposed to RT-PCR testing being used to test for COVID-19 before his death

CONCLUSION: All of these claims are INACCURATE.

The universal standard when testing for the virus that causes COVID-19 is to use a maximum of 40 cycles of amplification as part of the RT-PCR process. If a positive signal is detected with more than 40 cycles of amplification, this would be reported as a negative test. Neither of the claims about Kary Mullis are true.

Reverse transcription polymerase chain reaction (RT-PCR) is a laboratory technique used to test for a positive diagnosis of COVID-19. A Facebook post claims that the settings used can be made to generate a positive result: “[if] people test themselves … at say 60/65 cycles of amplification, then I will test positive and so will everyone else.” 

The post also attributes claims by the inventor of the RT-PCR testing technique: “Kary Mullis …  stated his test ‘cannot’ be used to diagnose infectious diseases at all … He was adamantly opposed to his test being used for Covid-19 right up to the point of his death.”

Claim 1: A high number of amplification cycles used in an RT-PCR test will lead to a positive diagnosis of COVID-19.

INACCURATE. Real-time RT-PCR (reverse transcription-polymerase chain reaction) is the preferred method of testing for a positive diagnosis of COVID-19 in the NHS, as is the case across the world. It is one of the fastest and most accurate laboratory methods for detecting the SARS-CoV-2 coronavirus, the virus that causes COVID-19.

Viruses contain genetic material: either deoxyribonucleic acid (DNA) or ribonucleic acid (RNA). The virus that causes COVID-19 only contains RNA, and spreads by infecting healthy cells and altering them so that they start creating copies of the virus.

In order to detect a virus like the one that causes COVID-19, firstly scientists need to convert the RNA to DNA using a process called “reverse transcription”. This is because only DNA can be copied (or “amplified”), which is a key part of how the real time RT-PCR process works.

A sample will be collected from parts of the body where the virus gathers, such as a person’s nose or throat. This sample will be treated with chemicals to remove substances such as proteins and fats, until only genetic material is left: DNA, RNA, messenger RNA.

This sample will contain the person’s genetic material and, if present, the RNA of the virus. This RNA is then reverse transcribed to DNA. Short fragments of DNA are added to the sample which will, if the virus is present, make the viral DNA multiply. The sample is then placed in a RT-PCR machine.

The RT-PCR machine will cycle through temperatures that heat and cool the sample to trigger chemical reactions that will cause the target viral DNA, if present, to create an identical copy of itself. Each cycle will cause the amount of viral DNA to double, so the second cycle will create four times the amount of viral DNA, the third cycle eight times as much, and so on.

Typically the process is to go through 40 cycles, which will create billions of copies of any viral DNA strand in the sample. As new copies of viral DNA are made, these will release a fluorescent dye, which can be monitored in real time by the person running the test.

When a certain level of fluorescence is met, this tells the scientist running the test that viral RNA was present in the original sample. The number of cycles required before the virus can be identified is known as the cycle threshold (Ct).

It was claimed that anyone can generate a positive test by running 60/65 cycles of amplification, instead of 40 as usual. This is not accurate. The summary table of available protocols held by the WHO contains testing RT-PCR protocols from China, France, the United States, Japan, Hong Kong and Germany.

These protocols  state that the maximum number of cycles is 40, with many also stipulating that a Ct of 38, 39 or 40 is an ambiguous result. Tests carried out by the NHS in the UK where the Ct is over 40 are held and not notified.

As a positive test will only be notified where the Ct is 40 or lower, a situation would not arise where over 60 cycles of amplification would be carried out, and these would not be considered a positive test result in the UK or elsewhere.

Claim 2: Kary Mullis, inventor of the PCR technique, said that the RT PCR “can not be used to diagnose infectious diseases at all”.

Reuters fact checkers found that the quote undermining PCR tests was misattributed to Mullis, and was taken out of context; the claim is inaccurate.

Claim 3: Kary Mullis was opposed to RT-PCR testing being used to test for COVID-19 before his death.

INACCURATE. Kary Mullis died on 7 August 2019, months before the first case of COVID-19 was reported to the World Health Organization in December of that year.


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