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LAMP-based Test Could Enable Point-of-Care COVID-19 Testing

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Testing is an important tool in the fight against the COVID-19 pandemic. Identifying and isolating infected individuals and tracing those they have been in contact with, is crucial to reduce spread of SARS-CoV-2. Currently, testing for active infection largely relies on qPCR, but the method is not without limitations. Alternative approaches are widely being pursued, particularly those that could be used at the point-of-care.

One such test currently in development is the RapiPREP® COVID-19 test, produced by MicrosensDx. The test, which is based on LAMP technology rather than PCR, has recently been assessed for clinical performance as part of the validation data that will allow MicrosensDx to complete the CE marking process.

Technology Networks spoke to Dr Christopher Stanley, CEO of MicrosensDx, to learn more about the RapiPREP® COVID-19 test, the results of the trial, and the difference point-of-care testing could make to the response to the pandemic.

Anna MacDonald (AM): Many of the current diagnostic tests for infectious diseases such as COVID-19 are PCR-based. Why is this method currently the “gold standard” and what are some of the limitations associated with it?

Christopher Stanley (CS):
PCR dominates the molecular testing field. It was the first nucleic acid amplification and detection method to be developed, so every diagnostics lab will have at least one of them. The technique has been finely tuned over decades and many testing laboratories are running PCR at the limits of its performance in order to get the highest possible sensitivity of detection.

One of problems is that it can be slow. The thermal cycling needed to amplify the nucleic acid fragments to detectable levels can take up to 2 hrs and this is the rate limiting factor.

PCR is also extremely sensitive to inhibition by contaminants from the sample and this places great emphasis on getting the sample preparation absolutely right.

AM: How does the RapiPREP® COVID-19 test work? Can you explain to readers who may be unfamiliar what LAMP detection is?

The RapiPREP® COVID-19 kit has two component parts: the first is a sample preparation to extract viral RNA from a swab and the second is the loop-mediated isothermal amplification (LAMP) and detection.

Sample preparation uses surface-modified magnetic beads that have a very high affinity for nucleic acids. Viral RNA capture is very rapid, followed by a wash to remove any inhibitors present, then the RNA is extracted using heat. This sample preparation step is fast, very efficient and delivers a concentrated solution of purified RNA to a modified LAMP reaction.

We use LAMP because it is far more resistant to sample inhibition than PCR and it can accommodate a large sample volume. The more sample we can add, the more RNA we will have to amplify.

We detect the LAMP reaction products using a fluorescent dye; the amplification chemistry is more complex than PCR (we use 8 primers) but as LAMP is isothermal, it does not have the delays associated with thermal cycling.

AM: What advantages does this method offer?

The RapiPREP® COVID-19 test has been shown in a clinical study to have equivalent accuracy and sensitivity to laboratory PCR methods whilst offering a considerable timesaving for diagnosis: generally over 2 hours for a PCR-based system, including swab processing, and <30 minutes for the full RapiPREP® COVID-19 test, also including swab processing. In cases where the patient has a high viral load our kit can show a positive result in less than 10 minutes.

The RapiPREP® test is a patient-side or point-of-care kit which can be used, with minimal training, in the care homes, clinics or in the community to rapidly detect who has the virus.

The kit is based on well-established technology - we already have commercial products which use the RapiPREP® system for the detection of tuberculosis.

AM: How does the test minimize the risk of false negatives?

The sample preparation “front end” processes a much larger quantity of sample than other methods and therefore delivers much more viral RNA to the LAMP reaction.  This then incorporates a proprietary control reaction using a synthetic target and different primers. This acts as a confirmation that the LAMP chemistry is indeed functioning and viral RNA is not present, hence a “true negative” control is built into the test.

AM: The test was
recently assessed for clinical performance.* Can you tell us more about this and the findings?

The findings have now been published by King's College London (KCL) and MicrosensDx as a pre-print. Sensitivity was 80% against a laboratory PCR test, the latter using two swabs taken on separate days - a “super gold standard.” The KCL researchers and clinicians were happy with the RapiPREP® COVID-19 single swab performance. The new test also detected patients who had mild clinical signs of COVID-19 but were negative by the laboratory “two swab” PCR.

Professor Tim Spector, Founder of the COVID-19 symptom tracker app JoinZOE and lead researcher in the clinical study, commented: “We have been very excited by how the RapiPREP® COVID-19 test has performed in our clinical study, exceeding our expectations. Its ability to rapidly and accurately test for infection at a point of care level has the potential to transform traditional COVID-19 detection methods."

AM: What are the next steps before the test can be widely distributed in hospitals?

It is simply a matter of manufacturing scale up and obtaining fast track approval for professional use from the MHRA, followed by CE certification in due course. We aim to have products available for distribution by the end of April.

AM: What difference could a rapid, point-of-care test such as the one you are developing make to the global response to the COVID-19 pandemic?

CS: Testing that allows rapid confirmation of the presence or absence of the disease, particularly in its early stages, will allow effective isolation of those infected, or confirmation that the person can continue working. This is particularly important to the NHS and to companies who wish to test their key staff. People who are exhibiting mild respiratory symptoms can also get very rapid reassurance that they are not infected with the virus. As new drug treatments for COVID-19 become available, a rapid patient-side test can act as a companion diagnostic.

Dr Christopher Stanley was speaking to Anna MacDonald, Science Writer, Technology Networks.

*This article is based on research findings that are yet to be peer-reviewed. Results are therefore regarded as preliminary and should be interpreted as such. Find out about the role of the peer review process in research
here. For further information, please contact the cited source.