My sister-in-law works for a company that ordered the FaStep Rapid Diagnostic Test to test their employees who have to go to the office. She sent my wife the instructions and this looks to me like an antibody test. Is it possible to use this to detect active infections? Or did her company just waste money?

Kind of.

There are different types of antibodies.

IgM - antibodies are the rapid response antibodies produced when currently infected

igG antibodies are those that are produced post infection to maintain some immunity.

I haven't heard of that test, but almost anything that is "rapid" is junk. I would guess that these are similar to a pregnancy test. Drop of blood and a rapid result line to read. I wouldn't trust the results...


Eta- I'm not a doc, just deal a lot with blood and Tests.

Meh...kinda I guess if the test is sensitive. I thought all antibody tests were poor



My wife has been tested for west Nile a few times and she hasn't converted to IgG so she's still actively infected for example. That was after 3 months

Not really. Depending on the quality of the test, there might be a 1-3 day period where the test might pick up antibodies during the end of an active infection, but unlikely.

An antibody test won't tell you when you were infected, only if you have developed antibodies. So even if positive, it's kind of useless for the company's purposes (unless the policy is to allow anyone who may have had an infection in the past to return). Likewise, if negative, it doesn't rule out active infection.

IgG can start showing up around 10 days after exposure, and IgM can sometimes be suppressed. The EUA says plainly that theses tests should NOT be relied upon to determine active Covid infection. Are hospitals following the EUA? No.

We are using a rapid antibody test on admit. If IgG and IgM are negative, only then do we do a PCR.

If IgM is positive, then we treat it as a "probable" case and don't confirm with PCR but treat as if it's active.

If IgG is positive with a negative IgM, then it's up to "clinical judgment" of the doctor to determine probable Covid status and they are being told to lean away from ordering a PCR to "save resources." If they previously tested positive on a prior visit a few months then it's an easy call. If they don't have a prior record of Covid, then it's all based on clinical judgement. Never mind the fact we have PCR testing available. Nope, we are going to use Tarot Cards and Magic 8 balls to make these decisions.

Missing some active cases, needlessly exposing staff on regular floors and delaying treatment of some older people. The biggest concern for me is the delay in care, could mean life or death for some of these folks. Having IgG antibodies (if the test is even accurate) usually means they've been exposed at least 10 or so days beforehand, so delaying care by another few days is a big deal.

That doesn't sound like a terrible strategy if PCR is in short supply.

I sincerely hope PCR is not in short supply anywhere in the country at this point.

I work in a molecular lab in Houston and since PCR tests are all so similar, they have us all rotating in to help with COVID testing.

I just wanted to add that not all rapid tests are antigen/antibody ones. I run the COVID-RAPID tests which has a 4hr turnaround time and is a crude PCR test (removes the RNA extraction step and has a shorter amplification time). The regular COVID PCR test at my hospital has a 24hr turnaround time.

There are a lot of different types (different machines/reagents) of regular COVID PCR tests. Our lab is validated for at least 3 of them because the supplies are often backordered so usually only 2 are able to run at a time.

I would agree that anything that has RAPID in it would not be very dependable but especially those that have results in less than 30min.