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What is the limit of detection of the KnowNowᵀᴹ Test?

The Limit of Detection (LoD) is the smallest amount of virus in a sample that a given device can consistently detect.

The Liverpool School of Tropical Medicine carried out an analytical study of the KnowNowᵀᴹ test, which determined that the LoD is 500 plaque-forming units per millilitre (PFU/ml). Based on accepted models of viral load in disease progression, this very low LoD suggests that the KnowNow test can detect infected people as early as day 3 to 4 of infection. This is before they become highly infectious, and a day or two earlier than most tests available.

In the absence of a single study that compares the LoD of KnowNowᵀᴹ to that of other tests, it is not possible to do a like-for-like comparison of the LoDs of different lateral flow tests determined by different studies. This is because there wouldn't be parity across cell cultures and strains of the virus used in the different studies. Additionally, it's important to consider that what the KnowNowᵀᴹ test detects is fundamentally different from other tests. KnowNowᵀᴹ is a true infectivity test which looks exclusively for the spike protein only present on active SARS-CoV-2 viruses. Whereas other lateral flow tests detect the nucleocapsid protein encapsulated in the centre of the virus, which can be present whether the virus is active or not.

The PFU/ml measure, as used in the Liverpool School of Tropical Medicine KnowNowᵀᴹ analytical study, is a measure of only the number of virus particles capable of forming plaques in a given sample - viral particles that are defective or which fail to infect their target cell will not produce a plaque and so are not counted by this measure. No inference can be made about the relationship of PFU to the overall number of viral particles in the sample, since this will differ from sample to sample.

Since the KnowNow test specifically detects infectious viral particles only, an LoD measured in PFU/ml is an informative and appropriate measure. However, for other lateral flow tests which indiscriminately detect active and inactive viral particles, an LoD referencing PFU/ml is not particularly informative or comparable to the KnowNowᵀᴹ LoD. For example, the sample used to determine LoD may have had a very low PFU/ml, but many inactive viral particles which were detected by the test. Ultimately, other lateral flow tests are not true tests for COVID infectivity, they do not detect only infectious virus like the KnowNowᵀᴹ test does.

If you'd like to read more about this subject, we recommend reading this paper. It argues that the "Limit of Detection matters and directly impacts efforts to identify, control, and contain outbreaks during this pandemic" since "higher LoD are likely to miss nonnegligible fractions of infected individuals." It also makes the case that LoD values for tests should be benchmarked against a universal standard and readily available in the public domain to enable like-for-like comparison of SARS-CoV-2 detection methods.

How specific is the KnowNowᵀᴹ Test?

The KnowNowᵀᴹ Test's specificity is 100%. In more than 700 negative patient saliva samples, it hasn’t returned a single false positive result.

This is so important for getting life back to normal. We don't want anyone to be stopped from going to work, heading off on holiday or socialising at events, when actually it would be perfectly safe for them to do these things.

Specificity is particularly important when disease prevalence is low and tests are intended to be used at enormous scale. For example, if a test with just a 3% false positive rate is used on one million people per day, that would result in 30,000 people per day being falsely identified as infectious with COVID-19 and being unnecessarily asked to self-isolate.

What is a KnowNowᵀᴹ Test?

The KnowNowᵀᴹ Test is the UK's only on-the-spot COVID-19 test that uses just your saliva to tell you if you are currently able to infect someone else with COVID-19.

Unlike other tests, the KnowNowᵀᴹ Test won't give you a positive result if you have been exposed to the SARS-CoV-2 virus in the past, but are no longer able to infect other people.

How big is a KnowNowᵀᴹ Test kit?

One box contains 25 tests, and measures 20cm (L) x 21cm (W) x 8cm (H).

Isn't lateral flow testing less good than PCR testing?

There have been questions raised around the sensitivity of rapid lateral flow antigen testing for SARS-CoV-2 as compared to PCR testing. However, these questions have been strongly challenged by the scientific community.

PCR tests identify the presence of the SARS-CoV-2 virus in the body, regardless of whether the virus is actively infectious. The PCR testing process amplifies the genetic code of the virus so that even minuscule amounts of the virus in the sample can be picked up. This makes for a powerful test, but since viral fragments can linger in the body for weeks even after the infection has cleared, infected individuals being tested using PCR will show as positive for a median period of 22–33 days in total. On the other hand, most people infected with SARS-CoV-2 are contagious only for 4–8 days.

So whilst PCR testing for SARS-CoV-2 may have been considered the "gold standard" test up until now, it will by definition show different results when compared to lateral flow tests which aim to identify individuals based on viral loads which suggest they are within their infectious window. This discrepancy between what each test is actually testing for has caused some issues where PCR testing has been used to evaluate the effectiveness of lateral flow tests, such as in the mass testing rolled out in Liverpool in November 2020.

The KnowNowᵀᴹ Test goes a step beyond other lateral flow tests with its unique, patented detection mechanism which only shows a positive result when live infectious virus is identified in the sample. As a result, PCR tests will similarly show different results to the KnowNowᵀᴹ Test in certain cases, since they will show positive results even for individuals outside of their infectious period.

For a much more comprehensive and referenced answer, you may like to read "Clarifying the evidence on SARS-CoV-2 antigen rapid tests in public health responses to COVID-19" from the Lancet.

Is it painful to take the KnowNowᵀᴹ Test?

No, not at all. It was really important to us when inventing this test, that it would be comfortable and easy enough that anyone would be happy to take a test every day if they needed to.

All the KnowNow test needs is a simple saliva sample from the mouth. Unlike alternative antigen tests or most PCR tests, the KnowNow test does not require the clinical professional to insert a swab very high inside the nose to collect a sample from the nasopharynx, nor does it require a tonsil swab. This is one COVID-19 test that won't make people gag or cry.

What does a positive test result look like and mean?

Positive KnowNowᵀᴹ Test result
Positive KnowNowᵀᴹ Test Result

If there is one red line visible next to the "C" in the KnowNowᵀᴹ device test results window, and any line at all, no matter how faint, appears next to the "T", then the test result is positive. This indicates that the SARS-CoV-2 antigen has been detected in the sample.

Following a positive result, current government guidance on matters including self-isolation and reporting the result should be followed.

What is a lateral flow test?

A lateral flow test is a simple diagnostic device designed to detect the presence or absence of a target substance in a liquid sample without the need for specialised and costly equipment.

The most commonly recognised type of lateral flow rapid test strip is the pregnancy test.

What's the long term vision for Vatic beyond COVID-19?

We’re focused on developing our predictive health technology and tests so that we can make medicine more proactive and help to predict illness before it becomes acute or infectious. We want to empower people to feel in charge of their own health and wellbeing by making testing more readily accessible and available, allowing for earlier prediction and prevention of acute illnesses.

Does the KnowNow Test identify all COVID-19 mutations?

The mechanism underpinning the KnowNowᵀᴹ test mimics the means through which the virus interacts with the surface of a human cell in order to detect it. As a result, we expect that it will continue to identify the SARS-CoV-2 virus even in the face of further potential mutation in the future, unlike tests based on antibodies.

We have modelled the difference between the Wuhan and 501Y mutations in a recombinant protein model to give us initial analytical evidence that the KnowNow test reacts to these variations of concern. And we are currently carrying out a study on live samples of these and other mutations to gather practical evidence of this.

In fact, we predict that the KnowNowᵀᴹ test may potentially become even more sensitive as the virus mutates to become more infectious. And we will continue to carry out further analyses and studies to support this prediction, and confirm that KnowNow continues to function on newer mutations as they arise.

Is it possible to tell if the test has been carried out incorrectly?

Failed KnowNowᵀᴹ Test Result
Failed KnowNowᵀᴹ Test Result

Yes, it will be very clear if the test has been carried out incorrectly and failed.

If there are no lines at all visible in the KnowNowᵀᴹ device test results window, then the test has failed, and it should be repeated with a new device and a fresh saliva sample.

Had COVID - 19 symptoms in the last 2 days? Apply here to help us make testing accessible to all.