Thread by @deeksj

@BBCr4today invited me to speak about lateral flow tests this morning (can listen at 0650). All government plans are now about using tests to "release" people - this depends on reliability of negative result. This is what the manufacturer says:

1/16

The PHE Porton Down - Oxford University report included this graph showing sensitivity would be 58% when the test is delivered by a trained test-and-trace centre staff member. This is in symptomatics - not asymptomatics.

2/16

The Government's 77% sensitivity combines the other two groups - tests done by Porton Down lab staff, and tests done by NIHR Research Nurses - i.e. the experts and completely ignores the 58% group. That seems completely wrong.

3/16

Remember that only 43 of the ~2500 people in the PHE Porton Down studies were asmyptomatic -data for other lateral flow tests shows they miss 10-20% more asymptomatic cases than symptomatic cases. So saying that we will miss at least 40% of cases seems very conservative.

4/16

This means negative results DO NOT RULE OUT INFECTION. THe risk of infection is probably halved in test negatives compared to the whole group.

Some might recall Dave Sackett's SnNOut - you need a high SeNsitivity test for a Negative result to rule Out infection.

5/16

Even the manufacturers are saying this - this is the third paragraph in their Instruction for Use sheet.

6/18

The argument that the infected cases that are missed are Not Infectious is a HOPE and not a FACT. There is no data to support this, and it will be incredibly difficult to do studies to establish this.

7/16

Because lateral flow tests are only positive when viral levels are really high, they miss people who never get that high, and are only positive in others on one or two days. PHE Porton Down said that the lowest level of detection for Innova was about equivalent to 25 Ct.

8/16

Now @DHSCgovuk @grantshapps @MattHancock @BorisJohnson and others are coming up with strategies using the negative results from asymptomatics in various strategies apparently TO KEEP US SAFE

9/16

The evidence is stacked against these working. They may detect a fraction of missed infections, but will not detect enough TO KEEP US SAFE

We need proper evidence based strategies to do this - based on understanding viral dynamics, and they will not work with these tests

10/16

The only answers @grantshapps had on @r4Today at 0824 - suggested we could confirm results with PCR (but if we are going to do that why use a lateral flow test??) and that the tests are getting better and better (really - I thought we had bought a lot of the same ones??)

11/16

Also that we have learned lots from Liverpool (what studies, what results, what research questions, what reports - please tell us too??)

Complete non-answers.

12/16

by the way, current WHO Guidance on Lateral Flow Tests says this, and the WHO EDL is likely to contain an explicit statement "negative tests cannot be used to rule out infection"

13/16

Feels like the Government is still in Pantomine season, they think that lateral flow tests are Cinderella's slipper and that we will soon reach the "Happily Ever After" page.

14/16

Its more like this (sorry trying to use as many media modes to get this important message over)

15/16

Lets stop the Pantomine and look at the clear evidence and use it.

Some of the audience won't be there for the "Happily Ever After" unless we do.

16/16