Theranos’ specific claim was that they could do existing tests with way less blood and way less cost. One of the ways they kept their fraud under wraps was to s

Theranos’ specific claim was that they could do existing tests with way less blood and way less cost. One of the ways they kept their fraud under wraps was to simply do the tests the old way behind the scenes. So, blood tests in general were not the controversial part of Theranos. As others have pointed out, the obstacles to large scale prophylactic blood testing are false positives, and general resistance of health insurers to fund anything not strictly reacting to disease or injury.