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World Health Organization Advises COVID-19 PCR Tests May be Giving Faulty or Skewed Results


Some tests are calibrated too high, causing positive results on non-infectious viral load


By:  David Deschesne

Fort Fairfield Journal, January 13, 2021


   The World Health Organization recently released new guidance on the use of RT-PCR tests for COVID-19, advising test administrators to be aware of the calibration settings of their testing systems because some are calibrated too high and thus keying positive on non-infectious viral fragments.

   A RT-PCR test has to amplify microscopic fragments of a pre-determined RNA fragment for a specific virus in order to detect it.  The more viral load a person has, the less the test will have to cycle copies to detect them.  Some tests are so sensitive, that they are keying positive on tiny amounts of non-infectious viral fragments that the person happens to have, but is not sick or contagious from.  These types of tests are akin to a common breathalyzer blood-alcohol test that does not display a percentage of blood/alcohol level but rather, simply says if a person has any alcohol in their body from a drink they may have had four or five days ago.  This is certainly no way to consider if a person is impaired from alcohol but it is how RT-PCR tests are being used to determine if someone is sick from COVID-19.

   The WHO statement advises, “Users of RT-PCR reagents should read the IFU [Instructions For Use] carefully to determine if manual adjustment of the PCR positivity threshold is necessary to account for any background noise which may lead to a specimen with a high cycle threshold (Ct) value being interpreted as a positive result.  The design principle of RT-PCR means that for patients with high levels of circulating virus (viral load), relatively few cycles will be needed to detect virus and so the Ct value will be low.  Conversely, when specimens return a high Ct value, it means that many cycles were required to detect the virus.  In some circumstances, the distinction between background noise and actual presence of the target virus is difficult to ascertain.”