Recently, a video of a German doctor named Claus Köhnlein was shared on WhatsApp and social media. In the video, Doctor Köhnlein claimed that the PCR test used in the diagnosis of Covid-19 was very likely to give false positive results, and the tests were unreliable. According to Köhnlein, these tests are very sensitive and the molecule of any substance can cause Covid-19 positive results. This does not mean that the person is sick. By saying this, Köhnlein concludes that the Covid-19 epidemic is exaggerated, and the threat is not as great as expected.
Polymerase chain reaction (PCR) is actually a technique used to “reproduce” small segments of genetic materials. One of the most important laboratory methods used to study the molecular fine structure of genetic material. This method is also used in the diagnosis of a large number of infectious diseases. Unlike serological tests, that is, the detection of antibodies developed by the body against the pathogen that causes a particular disease, PCR looks for the presence or absence of specific virus in samples taken in the laboratory. Swab samples from the nose and throat are taken for Covid-19 PCR tests. In these samples, the RNA structure that defines the virus is searched. PCR methods are therefore highly sensitive and are unlikely to identify the molecule of another substance since it looks at a specific RNA.
According to the World Health Organization, PCR test can be used reliably in Covid-19 detection. The Centers for Disease Control and Prevention also uses the PCR test in the diagnosis of Covid-19. Evrim Ağacı also considers RT-PCR tests as a reliable way to diagnose Covid-19. Because the test necessarily results in positive controls, negative controls and more than one repetition to increase its sensitivity.
Of course, PCR tests have an error level, but they are one of the most reliable tests currently known. The rapid diagnostic test and RT-PCR tests are different from each other. Rapid diagnostic tests have a higher margin of error. But if the PCR is done correctly, the margin of error is lower. Dr. Tayfun Uzbay, Head of Internal Medicine Department at Üsküdar University Faculty of Medicine, says that the PCR test is more reliable than rapid diagnostic tests and can be considered as the primary diagnostic test.
The accuracy of medical tests is determined by measuring two things: Sensitivity and specificity. While sensitivity indicates positive accuracy rate; the specificity measures true negative results. Laboratory tests determine a positive case (sensitivity) and a negative case (specificity). Therefore, it is less likely that a sensitive test will give a false negative result, that is, if you are infected, it is less likely that the result will be negative.
In a study, it is stated that testing samples from more than one region may increase sensitivity and decrease false negative test results. The clinical sensitivity of RT-PCR tests ranges from 66 to 80 percent. This means that about one in three people tested will get a false negative result.
The PCR test detects the presence of the virus, not its effectiveness. That is, even if the detected virus has lost its effectiveness, a positive result is obtained in the PCR test. In fact, the PCR test can be applied to surfaces exposed to Covid-19 or, for example, to sewage waters. In this case, even if the virus causing Covid-19 loses its effectiveness, the result is positive because its genetic material is detected. However, the virus is detected in swabs taken from a person and the result is very unlikely to give a false positive result.
Moreover, if the test was applied to the whole world and no false negative results were obtained and a high false positive result, the epidemic could be exaggerated as claimed by Claus Köhnlein. However, not everyone can be tested because the tests are done according to certain criteria. This means that not all existing positive cases can be detected.
Also, some studies reveal that if PCR tests are performed early during the incubation period, even if the person has Covid-19, it can give false negative results. Therefore, not only PCR testing is carried out on suspicious patients, but also their lungs are involved in the evaluation. So even if there are false positive results, this ratio can be said to be balanced with false negatives. Moreover, some people who have Covid-19 can survive the disease without showing any symptoms, that is, without being tested. In this case, contrary to what Dr. Köhnlein said, it is not possible to say that the PCR test shows people who do not have Covid-19 as if they are sick.
There is no scientifically agreed figure worldwide regarding the possibilities of PCR tests to give erroneous results. However, a study published in the British Medical Journal shows that out of 100 people who have undergone PCR tests under favorable conditions only one received false positive results.
Teyit reached the Science Board Member Alpay Azap to get information about the subject. Alpay Azap stated that PCR tests do not give false positives when working under ideal conditions. Since there may be erroneous results due to technical errors during the study of the test, the false positive and negative ratios may vary according to the centers where the PCR test is performed.
Similarly, virologist Kenan Midilli told Teyit that the PCR tests are reliable and that the tests are unlikely to give false positive results. Midilli stated that the tests that gave erroneous results were not PCR, but the tests made with antibodies from blood samples. According to him, the margin of error we should mention in this context should be false negative. In order to prevent false negative results, the tests are repeated periodically on suspicious patients.
In short, current data show that, contrary to Köhlein’s claims, the number of people who have Covid-19 infection is higher than the number of patients who have positive PCR tests.
The reasons for the wrong results of the tests may be taking the sample too early or late, contaminating the sample or waiting for a long time. Alpay Azap says that the sensitivity of the PCR tests performed in the second week decreases. Because the virus is located in the upper respiratory tract in the first weeks, but after the second week it descends into the lower respiratory tract. Azap states that even though the sensitivity rate of tests performed across Turkey is not known, PCR Covid-19 positive sensitivity is around 60 percent in Ankara University, where he works.
German verification platform Correctiv also reveals that Köhnlein’s claim is not true., , Alexander Dalpke, Director of the Institute of Medical Microbiology and Hygiene at Dresden Technical University, talked to Corrective and stated that there are no known false positive cases so far.
There is another situation that refutes Claus Köhnlein’s claim. One of the claims put forward by Dr. Claus Köhnlein was that Covid-19 is not a real disease and the world is exaggerating the epidemic. According to Köhnlein, if the Covid-19 test was removed, life would continue in its normal course. However, research to date shows that Covid-19 spreads more easily and has a higher mortality rate than flu. Also, antiviral medications work for seasonal flu, but there is no proven curative remedy or vaccine for Covid-19 yet.
The New York Times compares the number of people who died from Covid-19 to other deadly events in history. The new coronavirus is unlikely to kill about 50 million people worldwide, such as the 1918 Spanish flu, but it looks like it will have few competitors in the history of disasters considering the mortality rate. The increase in the number of people who died in New York due to Covid-19 in March was more than October 1918, the deadliest month in the Spanish flu period. Similarly, the death rate in London has tripled, and in Madrid, it has quintupled.
The page named Korona Gerçeği (Corona Truth), which has spread the video in Turkey containing allegations of the German doctor, is not credible either. Teyit had previously falsified the different claims shared by this page.
In conclusion, the claim that PCR based Covid-19 tests give 50 percent false positive results and tests are not reliable is not true. Contrary to Köhlein’s claims, the number of people suffering from Covid-19 infection is higher than the number of patients who had a positive PCR test. The post in question is an example of misleading content.
National Human Genome Research Institute, Polymerase Chain Reaction (PCR) Fact Sheet
Gesund Heit Laborbefund, Polymerase-Ketten-Reaktion (PCR)
World Health Organization, WHO lists two COVID-19 tests for emergency use, 7 April 2020
Centers for Disease Control and Prevention, CDC 2019-Novel Coronavirus (2019-nCoV)
Real-Time RT-PCR Diagnostic Panel, 30 March 2020
The Evolution Tree, The Safest Method in the Diagnosis of COVID-19: Quantitative Reversing-Transcriptase Polymerase Chain Reaction (QRT-PCR), 8 April 2020
Anadolu Agency, PCR test gives the most reliable result in the diagnosis of Covid-19, 2 April 2020
Pop Sci, COVID-19 tests are far from perfect, but accuracy isn’t the biggest problem, 7 May 2020
Arup Lab, How Accurate Are COVID-19 Tests? Many Factors Can Affect Sensitivity, Specificity of Test Results, 21 April 2020
HCP Live, Comparing RT-PCR and Chest CT for Diagnosing COVID-19, 17 March 2020
Hawk Environmental, PCR Testing (Surface, Molecular) For Coronavirus (SARS-COV-2)
ITN Online, COVID-19 Genetic PCR Tests Give False Negative Results if Used Too Early, 10 June 2020
American College of Cardiology, False-Negative Rate of RT-PCR SARS-CoV-2 Tests, 18 May 2020
Telephone conversation with Alpay Azap, 11 June 2020, 20.08
Telephone conversation with Kenan Midilli, 12 June 2020, 12.03
Roche Diagnostics, COVID-19 testing: What you need to know about test accuracy, 20 April 2020
YouTube, Prof. Dr. Alpay Azap Explains COVID 19 PCR Test, 24 April 2020
Correctiv, Coronavirus: Nein, aktuelle PCR-Tests haben keine Fehlerquote von 30 bis 50 Prozent, 7 April 2020
Twitter, Comparison of Covid-19 with other viruses, 13 March 2020
Hopkins Medicine, Coronavirus Disease 2019 etc. the Flu
New York Times, How the Coronavirus Compares With 100 Years of Deadly Events, 10 June 2020
Teyit, Two American doctors' claims regarding coronavirus, 20 May 2020
British Medical Journal, Interpreting a covid-19 test result, 12 May 2020
Want to support facts? You can donate to our cause at: https://destek.teyit.org
Follow us on Twitter:
Translation: Hilal Ebru Yakar