Labcorp/Roche Quantitative Antibody Data Points

[AsherO]

Imagine you found one of those old fashioned thermometers with a glass tube containing mercury, attached to a piece of plastic, but it's so old that the numbers and scale printed on the plastic have been rubbed off.  The mercury still rises with increases in temperature, so you can see that it's  warmer today than yesterday, but you don't know the exact temperature.  You lose that thermometer, but soon find another with the same problem.  Again, it can show relative changes in temperature over time, but you can't compare these values with those measured on the first thermometer because they may be using different scales, with different minimum and maximum and a different spread of the scale.  To make these thermometers useful, you could make a series of cups of water of known increasing temperature, place the thermometer in each one and re-create the scale on the thermometer. 

I’m loving the thermometer analogy.

Funny to see biobook schooling Bookish

[biobook]

BTW, this need to standardize different tests has occurred throughout history with all kinds of measurements.  My favorite illustration of this can be seen by visitors to Bologna.  In the 1300s, each merchant had a different standard for measuring length, so a customer could pay for 10 feet of fabric but get shortchanged because the merchant used a smaller "foot".  The city incised a standard foot measurement into the wall of the city, in effect telling visiting merchants: Wanna do business here?  This is how we define a legal foot. 
https://pauls-bologna.blog/2019/11/30/curiosities-of-bolognas-piazza-maggiore/

[biobook]

Funny to see biobook schooling Bookish

... and thinking, "Oh, I'm so jealous!  I wish I'd thought of that name first!"

[Euclid]

... and thinking, "Oh, I'm so jealous!  I wish I'd thought of that name first!"

@Bookisha is still available

[Bookish]

Thank you @biobook.  Yes, it was a different test, I don't know which, I only remember positive was over 15.  I was merely curious since 594 seems like such a high number that I was wondering if there was a reexposure that made the numbers go up. Or if that was considered lower than the 123 on the first test, as would be expected 7 months later.

The 2nd child was tested at least 6 times for covid and once for antibodies while our family was sick, and all were negative.  Interesting theory that she had it first, but we all tested for antibodies in January,  and that child was negative then as well.

Even if somehow she got it asymptomaticly months after us, I would think she would have higher antibodies than 1, so maybe the test being wrong is the most likely answer.

[biobook]

Even if somehow she got it asymptomaticly months after us, I would think she would have higher antibodies than 1, so maybe the test being wrong is the most likely answer.

Not necessarily.  If she had an asymptomatic case in March 2020, her antibodies may have significantly decreased by Jan 2021.

In any event, given what we know now about immunity, it would be expected that the rest of the family has good protection from reinfection for at least a year, but that this child should be considered unprotected (unless she's been vaccinated, of course) and vulnerable to infection, especially with the more-easily-transmitted Delta going around now.

[AsherO]

@Bookisha is still available

I grinned IRL

[Bookish]

Yes, but if she had it in March why would she have no antibodies in November and January but turn positive in July?  So unlikely that she had it then.

[biobook]

@Bookisha is still available

Okay, call me slow.  Took ten hours, but I finally got it. 

[biobook]

Yes, but if she had it in March why would she have no antibodies in November and January but turn positive in July?  So unlikely that she had it then.

The July test just barely crosses the threshold into the positive range.  According to one of the articles that compared different tests, the tests diverge the most in that lower range, so a barely-positive on one test could be negative on another.  If it's really bothering you, you could find out which test was used in January and retest with that same test now.

All this speculation is of theoretical interest, but not really of practical significance.  We just don't know enough about individual differences in antibody production to interpret this, and for that reason the CDC and FDA both discourage use of antibody testing at this point. 

https://www.fda.gov/medical-devices/safety-communications/antibody-testing-not-currently-recommended-assess-immunity-after-covid-19-vaccination-fda-safety

"Be aware that SARS-CoV-2 antibody tests help health care providers identify whether someone has antibodies to SARS-CoV-2, the virus that causes COVID-19, indicating a prior infection with the virus. However, more research is needed to understand the meaning of a positive or negative antibody test, beyond the presence or absence of antibodies, including in people who received a COVID-19 vaccination, in people who have been exposed and have SARS-CoV-2 antibodies, and in people who are not fully vaccinated."

[biobook]

I've said before that there's no point to testing for antibodies, because we don't know what level of antibody is needed for immunity, that is, to prevent a covid infection.  The recent report from Israel provides a bit of relevant data.  This is the study that was in the news for showing a small number of breakthrough infections in vaccinated people.  For a few of those breakthrough cases, the researchers had taken blood in the week before or on the first day of a positive covid test, so they could say something about what antibody level was insufficient to prevent a covid infection.  Those who got infections had lower antibodies ON AVERAGE than those who didn't, but the difference was not statistically significant. 

Covid-19 Breakthrough Infections in Vaccinated Health Care Workers
https://www.nejm.org/doi/full/10.1056/NEJMoa2109072

Scroll down to Figure 2, where the thick black horizontal line shows that the average antibody levels for breakthrough cases are lower than the average for controls.  But the dots and squares show the values for the individuals in each of those groups, and there's clearly a lot of overlap.

Don't ask me to explain the article, which I didn't understand myself.  Here are some reader-friendly summaries:
https://www.nature.com/articles/d41586-021-02096-3
https://www.cidrap.umn.edu/news-perspective/2021/07/israeli-study-finds-26-covid-breakthrough-infection-rate

[chff]

Lapcorp antibody 200 is high?

[AsherO]

Seems like they must have raised the upper limit sometime recently.

And again?



This is why I wouldn’t rush to get a booster even if I’m eligible.

[Moshe123]

That's definitely high. How recent was your last shot / infection?

[Euclid]

That's definitely high. How recent was your last shot / infection?

And if it was a shot - which one did you get?

[AsherO]

That's definitely high. How recent was your last shot / infection?

COVID+ Early February 2021
Pfizer 1st dose - Mid April
Pfizer 2nd dose early May

I also have a J&J daily with breakfast

Edited to clarify that my infection was in 2021.

[Moshe123]

COVID+ Early February
Pfizer 1st dose - Mid April
Pfizer 2nd dose early May

I also have a J&J daily with breakfast

So it's not even unusual.

[AsherO]

So it's not even unusual.

No idea. It could also be exposure as there's been a local uptick over the Tishrei holidays. For all I know I had a super-mild symptomatic reinfection, though that's unlikely because I tested negative on a rapid during peak symptoms. Also, no one who's been extensively exposed to me got sick.

[Bookish]

Jut to update since this thread got bumped, the child with 1 antibody has covid now.

[m.m.]

No idea. It could also be exposure as there's been a local uptick over the Tishrei holidays. For all I know I had a super-mild symptomatic reinfection, though that's unlikely because I tested negative on a rapid during peak symptoms. Also, no one who's been extensively exposed to me got sick.

From what I am hearing from people who were positive recently, it never was positive on the rapid, to the extent that maybe the rapid doesn't pick up the delta variant, or which ever one it was (not that it was extensive research, but 4-5 people that I know of personally).