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Trevor Klee's avatar

Great list! In terms of capillary vs. blood draws, I've been dealing that issue for NeutraOat. The standard is in-laboratory serum-based PFAS measurements, but at-home capillary PFAS measurements are becoming more popular. We are using capillary for our pilot study (pilot.neutraoat.com) .

I've been thinking a lot about the relative reliability of each, and how to convert between the two. The standard conversion factor in PFAS-world between capillary and serum is 2x based on the one formal study that's been done on converting between the two, which is off from what we are seeing in the field, which looks more like 2.56x. I'm not even confident there's a reliable conversion factor for every person, because capillary is so much messier than serum. Hematocrit becomes a bigger issue, for one thing, because hydration and blood flow affects capillary blood volume way more than serum.

More broadly, questions about capillary vs. serum start to become a broader question of what we actually want to know. We use capillary PFAS to convert to serum PFAS to convert to some broad band of threshold danger for increased risk of bad health effects, which all just collapses down into a binary question of "Doc, should I be worried?", or, for our case, "So are we actually seeing a real PFAS decline or not?" The patient doesn't care what the actual value is beyond that, so then it's unclear how much we, as scientists, should care about the relative accuracy of the tests. I know scientists hate philosophy, but the epistemology starts to become a real issue!

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