What law of physics makes what Theranos attempted to achieve impossible? They were still drawing blood from the patient. Thus, it seems theoretically possible for technology to overcome the challenges the approach presents.
> The blood you get from a prick will be a mixture of blood from small venules, small arterioles, capillaries and lymph vessels, mixed with whatever loose tissue and cells have been cut by the prick and carried over into the blood. No way you could ever get a reliable CBC from such a sample. Since the kind of general blood tests that this company is targeting are usually CBC + chem panel, even if you could get your chem results from the prick, you still need a normal blood draw for the CBC, so the competitive advantage that they are trying to push (quick sampling by patient at pharmacy, without need for phlebotomist) is lost. On top of that, the variability inherent in chem results from prick blood will be significant for several analytes, like CK and AST (present in muscle so could be raised from prick injury), glucose and lipids (different levels in venous or arterial blood or lymph), etc…
In short, while it might be possible to reliably use only µL of blood for tests, using µL of blood for dozens of tests seems questionable, and the chosen blood source is likely to be mostly worthless.
That the uncertainty produced by the source chosen exceeds the acceptable variability in the results is an impossibility proof for a testing method relying exclusively on a single sample from that source having acceptable accuracy, since the accuracy of the test result cannot exceed the accuracy of the source used in representing the underlying measure.
For comparison, there is tremendous variation in the sound waves that humans recognize as the word "apple", but there are still systems that can filter out the relevant noise and identify the critical dimensions of variation.
Simply saying that the source is messy is not a proof that it's impossible to work around that.
This is a fundamental problem. You might luck into roughly correct results most of the time, but the basic nature of statistics is against you.
My point is only that there is no hard theory decrying this to be impossible in the same way that, say, computer scientists can prove that a problem is NP-complete.