..."The test the White House has been using has a high false rate; there have been staff members who tested positive who tested negative a short time later. And there have been questionable negatives." [
link to twitter.com (secure)]
Think they still use the Abbott IDNOW platform, which officially is great but hasn't been doing well with independent verification.
Quoting: Dutchy20 Apparantly the first test was antigen, second test PCR. So he's most likely negative because PCR have the higher accuracy. What I don't get is the PCR test was administered in the afternoon but they have the result back already? I thought it took 24 hours minimum to process a PCR test.
WHY would they not use the more accurate test (in the first place) on a governor or anyone at the White House? SMH.
Exactly. If Dutchy is right in what he says that the more accurate PCR test only takes 1-2 hours to process then why aren't they using that in the first place.
The rapid test (the one with lower level of accuracy) is cheaper I think. But c'mon, if the Governor was due to meet with the President just give him the PCR test. It turns out the rapid test gave a false positive, but it could just as well have been a false negative. (I think I've got that right Dutchy?)
Antigen tests are point of care. You take the sample apply it to a test strip or put the sample in a machine and you have a result. Takes ~15 minutes to get a result. And doesn't require many additional resources or staff. They test for the presence of specific proteins associated with the virus. You can easily do it routinely for anyone that comes into contact with someone. And running a single sample is feasible. But there are indeed more false results both ways.
PCR testing takes a sample, breaks down the envelope of the virus and then synthesizes the viral RNA with nucleic acid amplification if it is present. It's more resource intensive and you need trained lab techs working in a decently controlled environment.
- Take sample->Prepare the sample via reagents->Add the primer that copies the sequence over X cycles->Thermal Cycle the sample with the primer to stimulate the cycling.
It takes a bigger machine and more time but it's biggest limitation is that you need to do it in a controlled environment and preferably run larger batches of samples at the same time, you can setup a lab but you cannot easily move the lab and the machines/resources used are generally in short supply.
Antigen test (Costs $1-$10) -> Quick and easy to perform (15m-1hr at point of care) anywhere but less accurate, useful for quick results where ever you are. If you can test people daily you can negate the effect of false results. It's a bad test to determine if a single person is infected if used irregularly though. Where they are very useful is in I.E. a school/college where you have bubbles and can use them to screen a group to assess if there are infections present daily. One positive->PCR test the entire bubble to determine who/how many.
PCR tests (Costs $100 to run the test in a lab, not adding the cost of sample collection (Nurses/Storage of Samples/Transport of samples) -> Slower (processing the sample and cycling it takes 1-2 hrs, but the sample needs to be taken and transported to a lab, prepared, processed afterwards) and very hard to scale (finite number of PCR machines that require lab technicians, scaling up takes a large initial investment) but if the virus is present in sufficient amounts to signify active infection you will find it. Great for determining the presence of the virus in a single person at the point in time the sample was taken.
So Antigen tests are fast, cheap ($ and resources) and scalable at the cost of accuracy.
PCR testing is slower, expensive ($ and resources) and hard to scale but more accurate.
The entire accuracy discussion could easily extend this post to the length of a essay so i'll forego detailing it, both tests have their own limitations and short comings but PCR is more accurate then Antigen.
As for the decision in the white house? I think the speed is a important factor if someone needs to see El Presidente having a quick result can be important, waiting for 15 minutes for a result that is processed down the hall is easier then taking a sample sending it to the lab etc.
