A new, sensitive COVID-19 test produces sample-to-signal in under ten minutes

A new, sensitive COVID-19 test produces sample-to-signal in under ten minutes. Researchers from the University of Birmingham have confirmed the speed, accuracy and simplicity of a novel, highly sensitive testing method for COVID-19 that can be deployed at entertainment venues, airport arrival terminals, and in remote settings where clinical testing laboratories are not available.

The Birmingham COVID-19 test, called reverse transcription-free Exponential Amplification Reaction (RTF-EXPAR), gives a sample-to-signal time of under ten minutes, even for low viral levels where current lateral flow tests are less effective.

About PCR and LAMP tests

Both Polymerase Chain Reaction (PCR) and loop-mediated isothermal amplification (LAMP) tests detect viral RNA, which can be present in extremely low levels in swabs taken from the mouth and nose. These tests use a two-step process which involves first converting to RNA to DNA (a process called reverse transcription) and then ‘amplifying’ the material many times over so it can be detected in the sample.

The speed and sensitivity of the PCR, LAMP and lateral flow tests

According to professor Tim Dafforn “Both the reverse transcription and amplification steps slow down existing COVID assays that are based on nucleic acid detection, compared to antigen tests, such as lateral flow, which do not have these steps. However, while this makes lateral flow tests faster than those based on PCR and LAMP, in return they are typically less sensitive.

An ideal test would be one that is both sufficiently sensitive and speedy. The RTF-EXPAR, test achieves this goal.

How does the RTF-EXPAR test achieve both speed and sensitivity?

RTF-EXPAR achieves speed and sensitivity in two ways. Firstly the assay team designed a new RNA-to-DNA conversion step that avoids reverse transcription, making it reverse transcription-free (RTF). Secondly their amplification step to generate the read-out signal uses EXPAR, an alternative DNA amplification process to PCR and LAMP.

Professor Dafforn added: “EXPAR amplifies DNA at a single temperature, thus avoiding lengthy heating and cooling steps found in PCR. However, while LAMP also uses a single temperature for amplification, EXPAR is a simpler and a more direct process, in which much smaller strands are amplified. This makes EXPAR an even faster DNA amplification technique than not only PCR but also LAMP.”

How did the scientists show that the RTF-EXPAR test is as sensitive and faster than than PCR and LAMP tests?

The scientists used a three-way comparison study to confirm that the Exponential Amplification Reaction (EXPAR) method is just as sensitive, but faster, than both PCR and LAMP tests which are currently used in hospital settings. The Birmingham COVID-19 test, called RTF-EXPAR, gives a sample-to-signal time of under ten minutes, even for low viral levels where current lateral flow tests are less effective.

The analysis showed RTF-EXPAR’s sensitivity is equivalent to quantitative PCR testing, with a positive predictive value of 89%, and a negative predictive value of 93%. The team expects to publish the full results of this testing in the near future. 

More about the time to signal detection for PCR, LAN and RTF-EXPAR tests

RTF-EXPAR demonstrated significant improvements over both PCR and LAMP-based assays on time to signal detection as shown in the table below:

RNA concentrationPCR time to signal detectionLAMP time to signal detectionRTF-EXPAR time to signal detection
7.25 copies/µL (low)42.67 (± 0.47) mins11.25 (± 0.20) mins8.75 (± 0.35) mins
1450 copies/µL (high)34.00 (± 0.00) mins11.25 (± 0.20) mins3.08 (± 0.42) mins
Is the product already authorised and commercialised?

The product is not yet authorised or commercialised. The team is seeking commercial partners for rapid licensing, to make the RTF-EXPAR test as available as widely as possible.

Source: Med-Tech Innovation News website