The story of a single whistleblower who took on three hospital networks and recovered millions of dollars in health-care fraud settlements is a cautionary tale for health-care providers that must learn to take internal fraud reports seriously.

The actions were brought by Cecilia Guardiola—a registered nurse who worked in clinical documentation and case management for three health systems—and demonstrate that whistleblowers can be smart and persistent and raise fraud and abuse issues that health systems cannot afford to ignore. Whistleblowers...