[exelius]

There’s no benefit to doing so; and smaller vials are harder to preserve. Measurements on blood draws are not exact, and pre-measured preservatives in the vials and the blood have to be in the right ratios.

This is easier to do consistently in larger vials, reducing the error in this part of the process to acceptable levels. It’s the same reason why a recipe will normally be more consistent when making a larger batch.

So you could collect less, but the way the modern lab industry operates (collecting samples, preserving them, and shipping them to an offsite lab for analysis) there is little business benefit to using smaller collection vials.

[2YwaZHXV]

Ok, so you're giving a business reason to not collect smaller samples. Which is fine and totally valid. Theranos was under the impression that there was an untapped opportunity for smaller samples.

But, the wording of the parent comment was saying that it was supposedly clearly technically impossible because of the small sample size. The OP said "I just never, ever understood how the sampling rate could ever work" and "and this should've been screamingly obvious to everyone since the beginning." That seems very different from "this is a very hard problem due to X, Y, and Z", especially since commercial machines that everyone here gets blood results from are already only taking small samples from the collected vials so the biggest challenge just seems to be in the collection and transport.

I agree that everything is easier with a bigger collection size, however "hard" is different from impossible.

[ethbro]

Out of curiousity, how tight are the preservative:blood ratios before Bad Things (i.e. things that would invalidate the test results) start to happen?

[2YwaZHXV]

That's a good question. Looking at this: http://apps.who.int/iris/bitstream/10665/65957/1/WHO_DIL_LAB... for EDTA (a very common anticoagulant "preservative") it is 1.2 to 2.0 mg/mL, so a decent range. But, this is one source and it will also depend on what the test is looking for.