Thread by @deeksj

IMPORTANT: MHRA New standards for LFT self tests for SARS-CoV-2 in people without symptoms.

@MHRAgovuk just published new Target Product Profile.

This is a guidance document based upon the best available evidence and independent expert opinion.

1/12

gov.uk/government/pub…

Important to note that the MHRA see these tests as for detecting “Current Infection”. That is detecting active infection, but is bigger than checking whether people are infectious. It also includes people who are pre-infectious.

2/12

They give guidance on reference standards to detect this. There are challenges here in establishing scientifically valid clinical reference standards. RT-PCR is regarded as acceptable which is what most are using.

3/12

Document gives “desirable” and “acceptable” performance levels, and separates out roles of the tests for RED LIGHT and GREEN LIGHT purposes, as they require different performance levels.

This all makes good sense.

So how well do they say these tests need to work?

4/12

Sensitivity needs to be >=80% for red light tests and 97% for green light tests, or even better.

5/12

Minimum sample size 150 cases, and evaluating the test in the intended use population.

Emphasises importance of empirical evaluation of strategies of tests, not just evaluating them in models.
Echoes many comments made by @RoyalStatSoc in report.

6/12

rss.org.uk/RSS/media/File…

Notably these values are not reached by Innova – data are only available on 80 asymptomatic cases from Liverpool and Birmingham, with a much lower sensitivity and no data on self-testing.

7/12

Specificity requirements same for both uses, 99.5% acceptable 99.9% desirable. No problem for Innova on this one.

8/12

The guidance is very clear on the importance of strong study designs following the recommendations here.
bmj.com/content/372/bm…

Great to see the regulator championing the importance of real world studies over analytical laboratory evaluations.
 
9/12

Interestingly that this means MHRA do not regard the laboratory based studies planned by the Test Valdiation Group as acceptable evidence.

There are some troubling disconnects between TVG and MHRA in these docs. TVG seems out of step.

10/12

gov.uk/guidance/techn…

They do acknowledge that more rapid study designs can be used in a pandemic, but insist on immediate commencement of methodological strong evaluations most-marketing

This is all very welcome

11/12

This seems well thought through and justified (there's lots of maths at the back) to explicitly stating the evidence and performance levels we need.

It may be some while before tests are available at these standards,

but it is clear that poor tests won't do.

12/12

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