Does anyone know how long after exposure an antibody test will still show a positive? For example, if someone was exposed in February, would it still show up?

I was just about to start a thread on this. I tested positive June 13 and believe I was exposed 5-7 days prior. I lost smell about a week ago for 5-6 days and definitely had other symptoms, albeit mild.

Went tonight to a neighborhood "Clinica Hispanica" in shady part of Houston because it was $115 and you get 20 min results and it's hard to get tested anywhere else right now. Came back neg for Covid19 and neg antibodies. Wtf? I should definitely have them by now right? They kept stressing "now you can go back to work with this form" and I can't help but wonder if this place is fully legit or an operation to get low income people back to work...but that seems like crazy conspiracy level sh**.

How could we not have antibodies if it's been a few weeks since testing positive let alone exposure?

DuncanAg said:

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Most (if not all) of the urgent care clinic rapid Antibody tests are junk. You want to get a Quest or LabCorp IgG antibody serology test. If you book through Quest direct I believe it's $119 and requires a blood draw (not a finger stick). I believe it's 100% sensitivity and 99.6% specificity.

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Good to know thanks. I give blood once every few months. I don't know if they use quest or labcorp but everyone I've talked to said they take about a week for results but are accurate. Will prob do that tomorrow. Glad to test neg for the virus, but I 100% had that mofo and beat it.

The finger ***** tests give a false negative about 1/3 to 1/2 of the time, depending on the maker. Some of the better ones work correctly 9/10 times.

The other types of antibody tests (blood draws - ELISA, CLIA) are more reliable.

Edited for clarity.

When is it too soon for reliable antibody test results? Should be max of week or two after pt of infection right?

AstroAg17 said:

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From a paper:

In a recent study, of 535 plasma samples taken from 173 patients with SARS-CoV-2, the median seroconversion time for total antibody (Ab), IgM, and then IgG were day 11, day 12, and day 14, separately.

Using the SARS coronavirus as an example, IgM antibodies generally rise above the detectable threshold for these point-of-care tests in approximately 5 to 7 days after the initial onset of symptoms (assuming a patient does develop symptoms after infection). The IgM then remains above the detection threshold for 14 to 21 days from symptom onset. About midway through the rise and fall of IgM production, around day 14 after symptom onset, IgG will rise above detection levels. IgG production will generally continue to rise for 28 to 35 days after symptom onset, peaking around or after clinical recovery. IgG typically has a long half-life and will remain above detectable thresholds for months or even years after the resolution of infection.

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This is accurate. The only caveat is that what is considered detectable limits is probably not the detectable limits of your average doc in the box rapid test. Right now, those generally are going to require higher levels to indicate a positive. I think some are still picking up antibodies for non covid Corona viruses.

Nasal swabs are not antibody tests.

I got the IgG antibody test from LabCorp. They took blood. I was in and out in like 5 min and got my results two days later. It was negative, I was a bit surprised.

Per OP question, how long before it is not longer detectable with quality testing? It says it has long half life and could be months or years. Anything more specific?

SamjamAg said:

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Per OP question, how long before it is not longer detectable with quality testing? It says it has long half life and could be months or years. Anything more specific?

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IgG antibodies are usually a lifelong thing. However immunity to certain bacteria and viruses does wane over time. For example, people are often required to get mumps, measles, and rubella titers to check for sufficient levels of IgG to those illnesses these days instead of just getting a booster.

With most corona viruses it appears as though immunity does wane over time, a detectable antibody may not be sufficiently high to still be protective. And that's one of the concerns with pushing for herd immunity - we don't know how long titers will remain at a protective level.

So, to answer your question - to be determined by continued research.

Cheetah01 said:

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Does anyone know how long after exposure an antibody test will still show a positive? For example, if someone was exposed in February, would it still show up?

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I also believe that I had the Covid-19 in early February. I've been trying for the past 2 months to get an antibody test to confirm this. I finally was able to get an antibody test from the Red Cross by donating blood and it came back negative.

So, this raises a few questions:
1 - Is the antibody test administered by the Red Cross any good?
2 - If I had Covid-19 in February would I still show the antibodies in detectable amounts now?

Long story short, I'm wondering if I should continue to pursue finding a Quest Diagnostics antibody test.

In Spain, it looks like they're finding antibodies in only about 18% of folks who had symptoms that were a match for COVID-19.

https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)31483-5/fulltext