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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 does KnowNowᵀᴹ compare to COVID-19 antibody tests?

The KnowNowᵀᴹ Test and COVID-19 antibody tests test for completely different things.

Antibody tests identify whether someone has had coronavirus in the past, whereas the KnowNowᵀᴹ Test detects whether an individual is currently infectious.

Antibody testing involves detecting the immune response in the human body to having fought off a virus. These tests look for an antibody created in the bloodstream in response to the presence of a virus in that environment. This is useful when testing the effectiveness of a vaccine, or understanding how far and wide a virus has spread. However, it is of limited usefulness to individuals, as it is only able to identify whether an individual has fought off the SARS-CoV-2 virus in the past. It cannot effectively confirm whether they are currently infected, or infectious.

Do you identify infection in people who are asymptomatic?

The KnowNowᵀᴹ test's unique detection mechanism identifies the infectiousness of the people tested. As a result, from our modelling based on accepted and peer-reviewed scientific literature, the KnowNowᵀᴹ test will detect asymptomatic people who are infectious with COVID-19.

The KnowNowᵀᴹ test has an impressively low limit of detection for an on-the-spot equipment-less test, of between 50,000 and 200,000 viral copies per mL, and so it is sensitive enough to identify infectious asymptomatic carriers even if they have low viral loads.

As the KnowNowᵀᴹ Test makes testing quicker, easier and more accessible, more people can get tested on an ongoing basis. Regular testing improves the chances of picking up asymptomatic carriers. Since the KnowNowᵀᴹ Test can detect the virus on day 3 to 4 after infection, based on KnowNow's low limit of detection and accepted models of viral load in disease progression, it identifies these carriers before they’re at a high risk of infecting other people.

Testing to identify asymptomatic carriers is so important, since they make up a large proportion of people who are infectious and enable the virus to keep spreading. This narrative review of 16 clinical studies around the globe concludes that between 40-45% of those infected with SARS-CoV-2 never develop symptoms, and that these asymptomatic carriers can infect others for an extended period, perhaps longer than 14 days.

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.

How do I order tests?

We're so pleased that you'd like to order our KnowNowᵀᴹ Tests. At the moment we are running some pilots with a few key partners, before distributing our tests more widely.

Please fill in our form and our team will get back to you.

Are you taking shortcuts or risks by developing the KnowNowᵀᴹ Test so quickly?

No, we're not taking any shortcuts or risks. The KnowNowᵀᴹ test has been precisely developed, rigorously tested, and approved by the necessary bodies.

As with COVID vaccine development, the speed at which we’ve been able to move has been accelerated by the enhanced support and focus afforded to the sector by all stakeholders, such as the government, the pharmaceuticals industry, academic institutions and so on.

We have conducted two clinical studies. The first was a UK Government-based study across ten UK hospitals; the second was with Liverpool School of Tropical Medicine. We have also carried out our own analytical assessments, as well as two Public Health England analytical assessments.

The KnowNowᵀᴹ Test has been CE marked for professional use within a healthcare context and is approved by the UK's Medicines and Healthcare products Regulatory Agency (MHRA).

When do you recommend tests are performed?

We recommend that tests are performed at the earliest opportunity possible, to ensure that individuals in the workplace, venue or community don't come into contact with each other prior to testing.

There's no particular time of day that's best to perform a test. Although it is important that individuals haven't had anything to eat or drink, and haven't smoked, within the 30 minutes prior to taking the test.

I've already activated my sample pack

If you have already activated your sample pack please go to the activation link that we emailed to you. Alternatively, if you fill in your email again we will re-send the activation link to you.

Can anyone order KnowNowᵀᴹ Tests?

At the moment, KnowNowᵀᴹ Tests are for professional use only, meaning that they need to be administered by a trained healthcare professional. This means that we can take orders from organisations that have in-house or outsourced healthcare professionals who can perform the tests, or testing service providers.

However, since the KnowNowᵀᴹ Test needs just a saliva sample, it is much easier to administer effectively than other similar tests, and still return highly sensitive results. So we are investigating whether specially-trained, competent individuals could be approved to administer KnowNow tests as well.

We are also in the process of trialling and seeking approval for a variation of the KnowNow test which could be administered by individuals themselves.

How sensitive is the KnowNowᵀᴹ Test?

What’s important when it comes to sensitivity is how much virus needs to be present in the patient sample for the test to give a positive signal. This is known as the 'Limit of Detection', and we measure this rather than clinical sensitivity as it is much more informative.

Our Limit of Detection is between 50,000 and 200,000 viral copies per mL, making our test more sensitive than other rapid antigen tests available. The Abbott BinaxNow test, for example, needs 1,000,000 viral copies per mL in order to get a positive signal.

The KnowNowᵀᴹ Test's low Limit of Detection means it 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 (based on models of viral load in disease progression).

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 Limit of Detection values for tests using universal standard metrics should be readily available in the public domain to enable like-for-like comparison.

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.

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