Jason Grimsley, a pitcher for the Arizona Diamondbacks, was released by the team last week after telling investigators he used illegal performance-enhancing substances, including human growth hormone, to boost muscle mass. He picked the hormone, a recombinant, or genetically recreated, form of one that is naturally produced by the body, partly because he knew that it is not detectable by Major League Baseball's current tests, which use urine samples. The hormone can be uncovered in a blood test, which was introduced on a limited basis by the World Anti-Doping Agency at the 2004 Olympics. But amid concerns about the invasiveness...