We would love to hear your thoughts about our site and services, please take our survey here.
London South East prides itself on its community spirit, and in order to keep the chat section problem free, we ask all members to follow these simple rules. In these rules, we refer to ourselves as "we", "us", "our". The user of the website is referred to as "you" and "your".
By posting on our share chat boards you are agreeing to the following:
The IP address of all posts is recorded to aid in enforcing these conditions. As a user you agree to any information you have entered being stored in a database. You agree that we have the right to remove, edit, move or close any topic or board at any time should we see fit. You agree that we have the right to remove any post without notice. You agree that we have the right to suspend your account without notice.
Please note some users may not behave properly and may post content that is misleading, untrue or offensive.
It is not possible for us to fully monitor all content all of the time but where we have actually received notice of any content that is potentially misleading, untrue, offensive, unlawful, infringes third party rights or is potentially in breach of these terms and conditions, then we will review such content, decide whether to remove it from this website and act accordingly.
Premium Members are members that have a premium subscription with London South East. You can subscribe here.
London South East does not endorse such members, and posts should not be construed as advice and represent the opinions of the authors, not those of London South East Ltd, or its affiliates.
A recent clear and very interesting article, highlighting the challenge and difficulty of creating a quick and accurate antigen test which is also sensitive. Hence why the FDA's sensitivity target is only 80%, which means 1 in 5 tests comes back with a false negative.....
https://www.sciencemag.org/news/2020/05/coronavirus-antigen-tests-quick-and-cheap-too-often-wrong?utm_campaign=ScienceNow&utm_source=JHubbard&utm_medium=Facebook
KingKitega - I anticipate now that we will have little difficulty in meeting the FDA sensitivity requirements, as you indeed imply.
I note with interest the FDA refer to PCR as the "golden standard" against which other antigen tests should be compared.
Could affimer- based tests be even more sensitive at the lowest limits? !!
That could appear at first sight in the stats as a false-positive for the affimer test.
Intriguing.
Ah yes thanks for the reminder Chengdo4! In that case, I think we can be very sure detached proteins can indeed be detected in a LFD, and have a lower LOD as a result.
Also, I've been trying to work out the size of the spike protein vs Affimers. From what I read online, the spike protein is around 20nm in size, whilst the Affimer has a mass of 12-14kDa, which is just over 2nm in size. *IF* more than one affimer can bind to a spike protein, this raises the chance of detached spikes being picked up in a LFT - and lance lowers the LOD further.
@CautiousOptimist - I think it comes down to what viral load is present in people with symptoms. Looking at the FDA template for MOLECULAR manufacturers - which antigen tests are to be compared against - its says in Part J. PERFORMANCE EVALUATION, Section 4:
"At a minimum 30 natural (prospective or retrospective or leftover samples) positive clinical specimens should be collected from patients suspected of SARS-CoV-2 infection by the healthcare provider in the COVID-19 disease endemic region(s)."
So I take this as based on samples of people showing symptoms of COVID19, and not asymptomatic. So again it comes down to viral load. I remember Ophidian sharing (see his post 09 May 2020 23:53) a Lancet report on Hong Kong patients indicated salivary viral load was highest during the first week after symptom onset with median at 5.2log10 copies per ml or 158,000 copies per ml. Ophidian also mentioned the Zika viral load was 99,000 copies per ml, so by reference Avacta's LOD was at least 99,000 copies per ml in that case. So in summary - seems pretty positive!
Good research stanman and KingK. Thanks for sharing your summaries. This sounds like the probability of the Avacta test being very good and approved quickly is very high. With only 30 samples minimum required for approval I wouldn’t be surprised to hear that the test has been developed, performed well and was submitted for approval to the FDA. Big week for Avacta this one even if news doesn’t come until next week
Very informative, thanks! So I understand the LOD is determined as the lowest concentration of viral particles that achieves 19/20 or better detection. Whereas sensitivity (which must be >=80%) is based on 30+ real positive samples. Does this not mean that it is a bit of a lottery as to the actual viral load in the true positive samples? e.g. the same test could report a higher or lower sensitivity based on luck of the draw as to how many positive samples exceed the LOD?
Having read the template,, and re-read it again, I am mightily reassured that for an EUA it is not necessary to recruit hordes of positive patients to donate samples. Very few in fact.
I'm quite surprised, & I must say, relieved!
Hi Stan man
Thanks for this. I think someone has posted all the FDA and MHRA stuff earlier this week. Apologies I haven't got more than that.
I've spent some time wading around the FDA website looking at guidance for antigen test submission.
Eventually found this-!
"Antigen Template for Manufacturers"
If you're interested access this via this link :
https://tinyurl.com/wu8anl2
... and see under 'Antigen Template for Manufacturers (May 11,2020)'
Happy reading! May look for an equivalent guidance document for CE submission tomorrow unless someone else beats me to it!