Thread by @chadhayesmd

Biotech companies distributing rapid IgG/IgM test kits for SARS-CoV-2 🦠that provide results in as little as 10 minutes from a simple finger stick.

What could go wrong?

Well... 😬

These are being produced and released without sufficient testing or FDA approval. We don't have great data on how accurate the results are, and any data that we do have likely comes from the companies that are trying to sell them...

I'm not *saying* they'd intentionally fudge the numbers or present only their best data, but I'd be less than surprised.

These tests are different from the COVID-19 testing you've heard of so far. They don't look for RNA from the virus, but for antibodies in your blood.

That's really useful information. They look for 2 kinds of antibodies: IgM, which shows up soon after an infection and then fades over time; and IgM, which takes longer to show up, but sticks around for years (usually) to provide lasting immunity (hopefully).

We don't know yet how long immunity to COVID-19 lasts--people way smarter than me are working on that.

But in general, positive IgM would indicate a current or recent infection, and IgG would indicate that someone has been exposed in the past and is (presumably) immune.

This information could be extremely helpful. Widespread testing would allow us to get a better idea of how many people have truly been infected with this virus, to help define the case-fatality rate (percentage of people who get infected die).

It would also let us know how many people have been exposed and didn't develop symptoms, had mild symptoms, etc. It would let us know who's been infected in the past--there are experimental treatments looking at taking serum containing antibodies from people who have recovered...

And using it to treat people with severe infections. And we could also use that information to help guide decisions about people returning to work, etc.

But all that depends on having accurate information. And that's really important, especially when making life/death decisions.

One issue is that it's still unclear how protective the antibodies produced to this particular virus are, or how long they last.

The other is the tests themselves. Im avoiding complex statistical topics, but here's a basic chart.

If the tests were 100% accurate, we would have only true positives and true negatives. That would be ideal. But nothing is ideal, and these tests won't be perfect.

False negative results could happen if the patient is tested too early in the disease and hasn't made antibodies yet, or because the test isn't great at picking them up.

False negative results could provide reassurance that would encourage people to engage in behaviours that would expose other people to the virus. (Caring for an elderly family member, returning to work, etc.)

But right now we should all be staying home anyway.

False positives (potentially a cross-reaction with similar antibodies to another virus, or some other issue with the test itself) could be harmful as well.

If, say, a healthcare worker or first responder is thought to be immune to this virus, they could return to work...

where they could be exposed to the virus and get sick (or be infected with the virus without symptoms) themselves and then go on to spread it to other people. Not ideal.

And again, there's a lot of uncertainty about how protective these antibodies are and how long they last.

So while antibody testing will be really helpful, it's important to do it right, just like everything else. We have to do the science. It needs to be reviewed independently. And while sometimes fast-tracking is appropriate, it comes with significant risks.

Finally, even if the tests are reliable, until they are widely available, there should be significant oversight as to who gets them and when. Testing should be prioritized to groups where the results matter most or to research. Not sold on some startup's website.

In summary, we aren't there yet.

Stay home. Wash your hands. Don't touch your face. Look around for PPE and donate it to your local hospital. Check in with the ones you love.

Stay safe. 🖤

Dammit. IgG* takes longer to show up but sticks around...

Give me the edit button