Posts mislead on Covid-19 testing in South Korea

The claim was shared here on Facebook on June 8, 2021.

The post shows a graphic with Korean-language text that reads in part: “Covid positive diagnoses. The normal CT value is 15, but Korea’s average is 37.”

Image

Screenshot of the misleading post. Captured June 21, 2021.

“Ct value” -- or the cycle threshold value -- is a number used in RT-PCR tests to categorise the concentration of viral genetic material detected in a patient.

RT-PCR tests are widely used in South Korea to diagnose Covid-19.

The post suggests that South Korea's measurements for testing have inflated reported Covid-19 cases in the country.

As of June 23, South Korea has recorded more than 150,000 Covid-19 infections.

Identical claims were also shared in Facebook posts here, here, here and here. 

But the posts are misleading.

‘No universal value’

RT-PCR tests for Covid-19 have no “normal” Ct value as the misleading posts claim.

“There is no universal optimal cut-off Ct value. Each [testing kit] manufacturer chooses the cut-off number,” Professor Kwon Gye-cheol, chair of the Korea Society for Laboratory Medicine (KSLM), told AFP on June 21, 2021.

Ct values used in six approved RT-PCR testing kits in South Korea range from 35 to 40, according to KSLM here.

‘Gold standard’

RT-PCR tests are the “gold standard” in detecting Covid-19 according to credible global health agencies, according to international health authorities including the WHO and the US Centers for Disease and Control and Prevention (CDC).

Self-administered Covid-19 tests -- typically rapid antigen tests -- should be combined with RT-PCR tests to ensure accuracy, according to this South Korean government report.

AFP has previously debunked misleading claims about the accuracy of RT-PCR tests for diagnosing Covid-19 here, here and here.