I still remember getting our first kit, opening the instruction booklet, laying everything out in preparation and being extra careful to do as I was told by the instruction leaflet at the time of testing. Admittedly this conscientiousness didn’t last.
In my family, my kids struggled. Were they the exception or the rule?
The use of lateral flow tests during the pandemic
As previously part of the test and trace program, LFT distribution within the UK reached levels of 300 million per month. They have provided much needed confidence when we were told that we have been in close contact with infected people when we wanted to meet with others or as a way of escaping mandated isolation earlier than required.
In the UK, we simply needed to submit a quick online form and a box of LFTs was delivered to our front door as part of the test and trace system. Alternatively, we could pop into the local pharmacy where they would gladly give you a box or two of Coronavirus tests for free.
Many of us have since carried out more home LFTs than we can count. As regular testing became an everyday part of our routine, I know I’m not alone in admitting my family’s attention to cleanliness, sample preparation and accuracy have waned.
So, let’s look back at the impact of our actions, or to use the usability term, ‘misuses’ on the functionality of the diagnostic rapid tests.
Why is cleanliness important for lateral flow testing?
Fast forward 18 months and probably a hundred tests later and the kids are balancing the strip on the arm of the sofa, perhaps not bothering to wash their hands before opening these sensitive tests. But does it really matter?
Is the sample likely to get contaminated and give an incorrect result? To provide that answer, our diagnostics experts at Team Consulting explain that the main concern is cross contamination rather than contamination of an individual sample. For families testing all at once, washing hands between samples is more important than general cleanliness if we want to get the right result for each family member and ensure that we don’t transfer infection to each other. But there’s more that can go wrong, especially when taking the sample.
Ensuring correct sample preparation for a COVID-19 test
I’m sure that I’m not the only parent with a negative experience of trying to shove a long stick towards the back of my child’s throat or up their nose for the first time. If you had told me that I would be doing it twice a week and my kids would tolerate it, I would never have believed you.
But are we getting ‘enough’ of the good stuff? How far up is far enough for a nose swab?
Well, for self-testing, this is where we are likely to make the most errors, along with the next two steps of mixing the sample with the solution in the extraction buffer tube and placing droplets on the strip. I didn’t even realise there was a potential for ‘over mixing’ a solution (excessive shearing forces breaking down the virus), or that putting an extra drop for good measure might cause ‘flooding’ and obscure the result and accuracy of tests.
These misuses may not apply to this specific test, but we need to be clear on the requirements, particularly if we are switching between test kits from different providers. For instance, one provider of LFTs stipulated that two drops were required, whereas another one mentioned four were needed.
Why should you wait to read your LFT result?
The fact that we could get a result quickly is important feedback for kids. It’s a clear yes or no, or at least has been for us so far. In the beginning, I would always leave the full 15 minutes before reading the result. More recently, I’ve left the house on the basis that I can’t see any trace of a second line within the first five minutes, asking my husband to call me on my journey if this changes.
So how important is this timing?
All the parameters of a lateral flow assay are optimised during their development, this includes the time to result. The time between applying the sample and getting the result allows the following processes to take place:
- When the sample is applied to the sample port, the liquid rehydrates the antibody conjugate which is in the pad below the port.
- The sample and conjugate can now mix. If there is any virus present, it will bind to the antibodies. This mix flows along the nitrocellulose membrane strip until it reaches the test line which is where the liquid/antibody conjugate will bind to another antibody and create a visual line. But the assay is not valid until the control line appears.
- It takes time for the virus and antibody conjugates to mix. Each assay will have unique kinetics, which influence the time an assay is ready to be read. Diagnostic assay developers will have carried out experimentation to determine the optimal time for reading the result.
- The consequence of reading too early is that insufficient time has been allowed for the binding to finish and a false negative result could be interpreted.
- If the test is read beyond the recommended time, faint lines may appear on the test line and could be interpreted as a false positive. These faint lines can appear due to the sample/conjugate mix being generally quite sticky.
How does reporting your test result help?
Data related to COVID-19 has exploded and I’m sure there will be many researchers doing PhDs trying to figure out where the primary sources of transmission lay or what degrees of lockdown worked or didn’t work to keep the number of cases as low as possible. But does more data actually help with this?
Although more data may help epidemiologically by reducing the impact of future viruses, the fact that reporting was optional means that the potential for skewed data is high. This is why controlled studies such as those conducted by the Office for National Statistics can be more helpful and reliable.
Are we fed up of too much packaging on diagnostic devices?
The waste generated during COVID-19 has been enormous. The little bags provided with each lateral flow device that we put directly in the bin, or keep just in case, are a source of frustration for me and probably for many others. As a nation, and particularly in my household, we’re aiming to reduce our single use plastics, yet many of these LFTs plastic bags are not even getting used once. I understand that we don’t want cross-contamination to occur or possibly infect our refuse collectors, but is this any different from putting a used tissue directly into the bin?
The simple answer is that for initial risk purposes, this is how they were designed and this is how they have remained. I would hope that smarter use of packaging will become a priority for future virus testing kits, reducing their environmental burden.
Different manufacturers, same system
Anything to make life easier when self-testing a family during busy periods is a win in my book, so the LFTs that came with the solution already in the mixing tube were surely a winner. But do these have any other benefits?
In pre-COVID times, where mass LFTs were not available, the buffer solution would typically be in a separate bottle and the user would be asked to transfer a few drops to the mixing tube. But as the test strips are optimised for a specific volume of fluid, errors in this step may impact results. The secondary benefit of this system is the ability to maintain sterility of the extraction buffer tube.
The inconsistencies between providers of LFTs with different use steps including varied droplet numbers and swab locations (nose and throat or just the nose) can cause confusion. To reduce use errors, tests should be made with the exact same steps.
Although LFT guidelines may have changed, looking back I can confidently say that I have learned a lot from this experience. Apart from the obvious personal learning for my family of ‘always reading the instructions’, I hope we can learn so much more from this unusual exposure to daily testing and diagnostics – leading us to develop systems that are usable, sustainable, and robust for all users.