WHO: PCR inaccuracy increases when disease prevalence decreases

World Health Organization clarifies that predictive value of PCR tests goes down as prevalence of Covid-19 decreases.

Arutz Sheva Staff ,

Technician checks COVID-19 tests
Technician checks COVID-19 tests
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The World Health Organization yesterday issued a new information notice regarding the PCR test being used to diagnose COVID-19 infection.

"WHO reminds In Vitro Diagnostic Medical Device (IVD) users that disease prevalence alters the predictive value of test results; as disease prevalence decreases, the risk of false positive increases. This means that the probability that a person who has a positive result (SARS-CoV-2 detected) is truly infected with SARS-CoV-2 decreases as prevalence decreases, irrespective of the claimed specificity.

"Most PCR assays are indicated as an aid for diagnosis, therefore, health care providers must consider any result in combination with timing of sampling, specimen type, assay specifics, clinical observations, patient history, confirmed status of any contacts, and epidemiological information," wrote the WHO.

Some scientists and experts have increasing warned that the PCR test does not give an accurate indication of coronavirus morbidity, saying that a positive PCR test does not necessarily mean the virus is present, infectious, or viable, nor does the PCR test detect the whole virus.



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