Take note - @dhscgov rapid tests are being sent out (certainly in schools) with two different (and conflicting) information sheets, one in the box and one given out separately.

(the crumpled one with the picture is in the box, the glossy one is handed out separately).

1/10
The clue to which one is most up to date is on the back page (the one in the box is the out of date version).

2/10
The important difference in on page 2, which has far more info in the box (1st) version than the version given out about who should use the test and what they should do.

3/10
The box version states "You can use this self-test kit if you have symptoms or if your are asymptomatic (you do not have symptoms)"

There is no equivalent statement in the new guidance. (it states on p3 that you should refer to NHS guidance online if you have symptoms).

4/10
The "what your results mean" section has moved to page 16 in the new booklet

5/10
The original version (in the box) gives no clear directions on what the results mean and what you should do. There is no instruction to isolate with a positive result or to maintain social distancing with a negative result.

It really did need changing.
6/10
The new version is much clearer - "should" has been changed to "must" for both positive (isolate) and negative (continue social distancing etc).

7/10
But giving everybody two different leaflets is clearly going to cause massive confusion. And there seems little doubt that "the one on the box" is the one people will be able to find most easily.

8/10
@MHRAgovuk is this acceptable to distribute a test providing a outdated instructions for use document? We would never allow this for a drug.

9/10
For added confusion the boxes also contain this note from Xiamen saying that they are for use in "individuals who are suspected of COVID-19 by their healthcare provider".

10/10

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More from @deeksj

6 Apr
@drdavideyre isn't the 89.5% figure based on the samples in symptomatic index cases taken at the test-and-trace centre? So this shows how good the test works in those who attend test-and-trace with symptoms? Pretty good idea to use them there.
Using this test (or better ones) backed with PCR in test-and-trace centres could revolutionize contact tracing- if people get their results and meet with an infection control team before they leave the centre we will be moving everything forward 3 days. Add in financial help too.
But how well they work in mass testing or contacts will depend on the distribution of viral loads in these groups - which I cannot see that you have any data on in this paper. The Cochrane review showed sensitivity much lower in those without symptoms.

cochranelibrary.com/cdsr/doi/10.10…
Read 5 tweets
30 Mar
Important paper in @bmj_latest from global leaders in test evaluation. Hope will improve quality of studies.
1/n

Guidance for the design and reporting of studies evaluating the clinical performance of tests for present or past SARS-CoV-2 infection bmj.com/content/372/bm…
Thanks to @JennyDoust @KatyJLBell @leeflang_m
@jacdinnes @SallyJLord @SueMallett Janneke van de Wijgert, Sverre Sandberg, Khosrow Adeli,@pmmbossuyt Andrea Horvath for working on this with me. Its a team which covers all important aspects of test evaluation.

2/n
From reading @DHSCgovuk @PHE_uk study reports and many others from organisations around the world, we are aware that the level of understanding about clinical test evaluation studies is often less than ideal.

This paper lays out clear steps to help improve.

3/n
Read 14 tweets
26 Mar
ONS just announced weekly infection rate in secondary school aged children is 0.43%.

Yesterday Test-and-Trace data showed 0.047% of LFTs were positive.

How can we get an estimate of the sensitivity of LFTs from this? I’ve come up with sensitivity=10%

Here are my workings
Three issues

#1 0.047% will include LFT false positives – 0.03% according to DHSC, so 0.017% will be LFT true positives.

#2 0.43% will include PCR false positives – lets go for 1 in 1000 (probably less) to be conservative. So 0.33% will be true cases
#3 ONS data are based on number of children, LFT on number of tests. If assume two tests per week (but only ever one positive per child) then double the rate to 0.034%

So sensitivity seems to be about 0.034/0.33 = 10%

Anybody else want to present a version of these figures?
Read 5 tweets
25 Mar
LFT test results for week to 17th Mar

Flatlining – few cases in schools - costing tons of money - causing many FPs

7.6M tests week, up from 6.3M
@£5 per test=£38M
@£20 (real cost reported from Wales)=£152M

To get 8279 +ve results (0.108% yellow line) many of which will be FP
What happened in secondary schools?

3.9M tests in students, 1805 positive results.

1 in 2140+ve (previous week 1 in 2070).

Would expect 1160 false+ve if 99.97% specificity (Government’s new claim)

64% of +ves were false+ve with kids+bubbles+families isolating unnecessarily
Overall we’ve been above 1000 tests to find one true positive for the past fortnight using the 99.97% specificity figure,

and for 3 weeks using the slightly 99.9% specificity figure.

“Finding needles in haystacks”
Read 5 tweets
24 Mar
Updated @cochranecollab review of Rapid Tests for Covid-19 is here

Rapid, point‐of‐care antigen and molecular‐based tests for diagnosis of SARS‐CoV‐2 infection - @jacdinnes @deeksj - 2021 | Cochrane Library

cochranelibrary.com/cdsr/doi/10.10…

1/12
Update included electronic searches to end of Sept, and other resource up to mid Nov 2020. Next update is already underway. Many thanks to the great crowd of people involved in putting this together.

2/12
Included both lateral flow antigen tests – data on 16 tests (of 92 with regulatory approval) in 48 studies (n=20,168)

And rapid molecular tests – data on 5 tests (of 43 with regulatory approval) in 30 studies (n=3,919)

3/12
Read 12 tweets
22 Mar
More disappointing data on sensitivity of LFT for mass testing - this time from Wales.

This report includes data from mass testing Nov-Dec
cwmtafmorgannwg.wales/whole-area-tes…

I think it is with Innova but report does not actually say.

(Note: sens/spec calculations in the report are wrong)
Data from Merthyr Tydfil

You can't compute sens and spec directly from this (but the authors did) as only 2.1% of LFT -ves were included compared to 42% of LFT +ves

Correcting for sampling fraction
sensitivity is 17.5%
specificty is 99.7%
Data from the lower Cynon Valley

Again their is a sampling issue with
4.1% of LFT-ves being verified compared with 59.1% of LFT +ves.

Sensitivity 25.6%
Specificity 99.6%
Read 4 tweets

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