Will next-generation COVID-19 tests replace standard PCR checks?

The  methods are evolving from the standard polymerase chain reaction (PCR)  test to the gene-editing CRISPR-based tests and next-generation rapid  diagnostic tests (RDTs) that single out a protein existing only in the  COVID-19 virus.

Celltrion recently said it was working on a  next-generation rapid detection for COVID-19. The conventional RDTs  detect the N protein commonly shown in various types of coronaviruses,  so patients need reverse transcription-polymerase chain reaction  (RT-PCR) test to confirm COVID-19 infection, said Seo Jung-jin, chairman  of Celltrion Group, in a live YouTube news conference on Monday.

However, Celltrion’s  experimental diagnostic kit detects the S protein that exists only in  the COVID-19 virus, which will show similar performance compared to the  standard PT-PCR test, he said. “We will be able to get the test result  in 15 or 20 minutes,” he added.

Usually, rapid diagnostic tests  use an antigen or an antibody so that the test results can come out  faster than the standard PCR test. However, their accuracy is only about  50 to 70 percent of the standard test. However, Celltrion’s new  diagnostic kit will be a new rapid diagnostic test with high precision,  Seo noted.

“The next-generation rapid diagnostic test kits will be able to replace PCR tests,” he said.

Celltrion  said it planned to complete producing prototype products by April,  finish a clinical trial by May, and get CE certification to export them  to Europe.

Local and U.S. biotech firms are also using the gene-editing tool, CRISPR, to detect the viral infection.

CRISPR-based  diagnostic kits use techniques similar to those of the PCR test, such  as the extraction and amplification of RNA. After extracting and  amplifying the RNA from the patient's sample, examiners add the guide  RNA to find the sequence of the COVID-19 genome. When CAS12 with the  guide RNA arrives at the corresponding sequence, it gives off a molecule  that changes color, which shows the positive result of the viral  infection.

One biotech firm in the U.S. tested the kit with a  COVID-19 patient’s sample, and it showed a similar accuracy to the  standard PCR test, news reports said. Using “Loop-Mediated Isothermal  Amplification” (LAMP) in the CRISPR-based test can detect the virus in  about 30 minutes, they said.

However, it is still questionable whether such experimental tests could replace the standard RT-PCR test, experts said.

Lee  Hyuk-min, director of infection control affairs at the Korean Society  for Laboratory Medicine, was skeptical about Celltrion’s next-generation  COVID-19 detection. “Even though they say they would detect the S  protein to raise sensitivity, the S protein is easily mutated,” Lee  said. “Antigen/antibody tests produce many variants, thus difficult to  control, compared to PCR tests.”

Lee pointed out that  CRISPR-based tests could raise sensitivity even higher than the PCR  test, but it would hinge on how they would be designed. As the current  PCR tests do not have sensitivity issues, companies would have to have  the right strategy because people need a test with the right level of  sensitivity so that the patient could get an urgent surgery, he added.

“Loop-mediated  isothermal amplification does not need complex equipment as PCR tests  do, so the method would be helpful to raise sensitivity and simplify  equipment,” Lee said.

Just like GeneXpert that obtained urgent  use approval in the U.S., emergency tests could be possible depending on  how companies design the “packaging” for the PCR test, he noted.

“Even  when companies have the same technique, they can produce very different  kits depending on their strategies. So, it is important to use the  right strategy.”

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