[conspire] Yet more on COVID-19 IgM testing challenges

[Deirdre Saoirse Moen]

Okay, there’s *definitely* anomalies here.

In addition to the previously-mentioned study:

1. …tests aren’t picking it up.

Brazil recently produced a report on the accuracy of their approved tests and it has a stunner of a line near the end:

https://www.sciencedirect.com/science/article/pii/S1413867020300295 <https://www.sciencedirect.com/science/article/pii/S1413867020300295>

"However, it is important to highlight that the rate of false negative results from tests which detect SARS-CoV-2 IgM antibodies, used for detection of COVID-19 in the acute phase, ranged from 10 to 44%.”

2. …because it’s not there.

https://www.medrxiv.org/content/10.1101/2020.05.18.20105155v1 <https://www.medrxiv.org/content/10.1101/2020.05.18.20105155v1>

Big long study (preprint) of 1850 pts from China (preprint) says that:

While IgM was rarely detected (32.5%) during the early stage (SupplementaryFigure S1B). 97.4% of the confirmed patients have positive IgM or IgG at the first 1 week after symptom onset, indicating that the combination of IgM and IgG is necessary for auxiliary diagnosis. (p.8)

So it seems the body’s compensating by producing IgG instead (makes sense) and the COVID-19 severity is correlated to certain measurable relationships between certain antibody levels. Which makes some sense. More interesting was that those relationships predicted hospital *readmission*.

We still don’t know what’s happening to the IgM. My leading suspicion is protein folding (since a molecule that is made correctly can be made to fold incorrectly, rendering it useless), but I could easily be wrong on that.

Deirdre
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