Thread by @fascinatorfun

Doctors condemn secrecy over false negative Covid-19 tests | World news | The Guardian

This is one of the reasons why diagnostic test results should be published by lab: positive/negative/ unclear/ age/sex/ethnicity/occupation/ care home. theguardian.com/world/2020/may…

It now looks as if 8 different test sets may be in use and that too should be an identifier.

To be clear. All over the world there are false negatives. Some far worse than this, including France, USA and Spain.

But if some test sets or labs or samples are markedly more accurate than others we should knows.

There is no 100% reliable test not least because the viral load changes over time. And people seek tests at different stages

This is a good explainer.

bmj.com/content/369/bm…

BUT if there is one or two kits or sets that produce more accurate results (not false negatives OR false positives) then it is clearly better to use those.

That is the point of quality control.

Or is the problem in the swabbing? The lab processing? Specific technicians?

If there are right quality control systems in place it should help prevent extended errors.

In France (where they were experiencing 30% or more false negatives) they recommended a CT scan when in doubt.

Ditto some hospitals in the USA said nearly 50% were false negatives.

So precision in datasets and data lines matter

Transparency matters.

And the protocol to be followed where there is reason to doubt the test result.

To be fair. This is a new virus. New test. New pandemic.

Even the best people are unlikely to be able to create perfect datasets and systems. Expect corrections.

But I do wonder if the new commercial tests are really equipped with the rich interconnected information systems so that all labs can compare test sets and performance

I would also point out that the research to which they point gives a far more nuanced picture of when and why false negatives occur, not least when in the progression of the virus the test is administered.

I have attached the study.

Another problem has been that reagents that would normally be reliable have been delivered sub standards to labs around the world. So labs have to test every batch to make sure they meet the description sold.

And swabs suitable for one test kit can be unsuitable for another (Many complaints about that in the USA).

So there may be many reasons why testing will produce false negatives. And, as the study points out, no test kit is 100% accurate.