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World Health Organization updates PCR test guidelines

The World Health Organization has updated their instructions on how to properly use polymerase chain reaction (PCR) tests for the detection of COVID-19.

PCR tests, seen as the “gold standard” for determining whether an individual is positive for COVID-19, use a nasal swab and are the most prevalent testing mechanism for the virus throughout much of the world. The updated guidelines from the WHO supersede its previous instructions released on Dec. 14, 2020.

In its description of the problem with PCR testing, the WHO suggests that those using these tests should follow its instructions for use when interpreting results for specimens using this methodology.

Users must read the instructions for use “carefully to determine if manual adjustment of the PCR positivity threshold is recommended by the manufacturer.”

“Careful interpretation of weak positive results is needed,” the WHO statement says. “The cycle threshold needed to detect virus is inversely proportional to the patient’s viral load.”

When test results do not correspond with clinical presentation — e.g. if a positive result did not correspond with other signs and symptoms of COVID-19 — the WHO is recommending that “a new specimen should be taken and retested using the same or different [nucleic acid testing] technology.”

The specialized agency of the United Nations focusing on international public health reminded users that “disease prevalence alters the predictive value of test results,” adding that “as prevalence decreases, the risk of false positives increases.”

Dr. David Samadi, a certified urologist and contributor to Newsmax, suggested that the changes were encouraging labs across the world to reduce their cycle count for PCR tests, stating that “the current cycle was much too high,” and that this “was resulting in any particle being declared a positive case.”

“The probability that a person who has a positive result [a detection of COVID-19] is truly infected with SARS-CoV-2 decreases as prevalence decreases, irrespective of the claimed specificity,” the updated WHO information states.

The WHO notice concluded by suggesting that “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.”




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