In both cases it's going to be statistical though. If you find one instance of a flaw in the Theranos it'll be easy to challenge it by talking about variations

In both cases it's going to be statistical though. If you find one instance of a flaw in the Theranos it'll be easy to challenge it by talking about variations in blood chemistry, blood draws, time of day, etc. Good controls can help, but unless you can bring a phlebotomist on site to wherever the Theranos is you're going to face external consistency issues. So the right answer is to repeat the experiment. Perhaps many times. You'll end up with a statistical judgement of consistent inaccuracy and while it'll be easier to prove (in terms of statistical strength) than showing accuracy, it'll still be (a) reasonably expensive, (b) generalizable research, and (c) less punchy for headlines. (b) is especially concerning because if you publish generalizable research involving humans, as would be the only way to do this, then you have to treat it like a legitimate clinical trial and are responsible for many more legal processes, e.g. IRB approval.