The company offers more than 240 tests, ranging from cholesterol to cancer. It claims its technology can work with just a finger prick. Investors have poured more than $400 million into Theranos, valuing it at $9 billion and her majority stake at more than half that. The 31-year-old Ms. Holmes's bold talk and black turtlenecks draw comparisons to Apple Inc. cofounder Steve Jobs.
But Theranos has struggled behind the scenes to turn the excitement over its technology into reality. At the end of 2014, the lab instrument developed as the linchpin of its strategy handled just a small fraction of the tests then sold to consumers, according to four former employees.