Antigen tests are positive when contagious and turn negative when infectiousness subsides... *** best thread on Twitter this month ***

[WVU82]

michael mina
· 6h
Maybe most important line in the paper:
“Although many caveats remain, the point in the course of the first week of symptoms at which AgPOCT results turn negative may thus indicate the time at which infectivity resolves.”

Antigen tests are positive when contagious and turn negative when infectiousness subsides

***Comparing Ag to PCR (which stays positive for weeks after infectiousness subsides) is NOT APPROPRIATE for evaluating a test meant to detect people who are infectious.

 

[WVU82]

michael mina
·
4h

PCR CAN be used as comparator - but must be w extreme care RNA presence does not = live virus presence It’s like faulting a newly installed security camera for not detecting a crime that was committed - even though some DNA is left on the floor at which it points.

 

[WVU82]

elon musk
·
3h

In your opinion, at what Ct number for the cov2 N1 gene should a PCR test probably be regarded as positive?

If I’m asking the wrong question, what is a better question?

 

[WVU82]

michael mina

Replying to
elon musk

Great question! It’s more complex question and depends on why the test is being used -

ie: do you want to know if you are currently contagious/risky to others or if you have any remnants of RNA?

The difference may sound trivial but it is massive

 

[WVU82]

michael mina

and
elon musk

If the question is "Am I currently infectious right now when the swab is collected" then on *most* instruments/labs, data suggests a Ct value somewhere around 30 or below is needed.
(Different instruments/labs are different - but that's a decent generalization)...

 

[WVU82]

michael mina
·
3h

If the question is "Am I becoming infectious" then even if you have a high Ct value... say 38... then it's important to test again the next day.

If you go to 28, then you better stay put, you're likely infectious for the next 5-8 days or so...

 

[WVU82]

michael mina
·
3h

If you stay at ~38 or you went from 32 to 35 or something over a 24 hour period - then most likely you are recovering from infection and no longer infectious.

Some people stay positive after infection with Cts in mid-upper 30's for weeks/months.

 

[WVU82]

michael mina
·
3h

If want to know if one is a danger to others RIGHT NOW... a rapid antigen test can be your best friend.

If positive, immediately confirm with a second *different* rapid test (antigen / lamp / isothermal) or get a PCR - but it has a long turnaround time so not as useful.

 

[WVU82]

michael mina
·
3h

If you just want to know the question that doctors often ask: "Do I have evidence of a SARS-CoV-2 infection" then look for the RNA with a PCR test or PCR-like test.

In this case, a Ct value <40 is usually considered reliable on most tests for "Do I have any virus RNA in me"..

 

[WVU82]

https://twitter.com/michaelmina_lab
stonkmanup
·
2h

Why are Ct values for tests not provided with the results?


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elonmusk
·
1h

They should be imo.

If you get a blood pressure test, they tell you the number, not just if it’s high/not-high.

There is not a clear consensus on what Ct value of what cov2 gene constitutes “positive”.

 

[WVU82]

minty_trades
·
3h

Replying to michael mina and elon musk

Rightfully so you can be Antigen Negative and PCR positive.

You can also have 4 tests with 50/50 results for a number of factors.

You shouldn’t have been tested using BDx4 should have been Abbott/BD/Sona Nanotech/Roche in order to get the most accurate picture of contagious state

 

[WVU82]

Biotechs_R_Us
·
3h

Replying to michael mina and elon musk

From a PK pov if the viral Ag is cleared from the host much more quickly than viral RNA, then assuming a high sensitivity a positive Ag test means a very active ongoing viral infection due to antigen shedding.

 

[WVU82]

minty_trades
·
3h

Exactly why we need Antigen testing for widespread screening use.... with proper protocols in place due to inevitable ‘false’ pos/neg results.

We are using spoons (PCR) to dig holes, when we have backhoes (Ag) ready to go.

Time for results > Accuracy.

Slovakia got it right...