Roche developed a treatment for a rare form of depression that kept patients feeling fine and kept them functioning normally. Sufferers greatly preferred this treatment over alternatives that would tend to put them into a near-catatonic stupor. However, for a subset of the population with high levels of a certain enzyme, the drug could cause permanent damage and death. So Roche required regular blood tests, and refused to sell to any patients who's levels of this enzyme became elevated. Many blood labs sued to be allowed to perform these blood tests. Why was Roche reluctant to allow third-party blood tests?