A widely used software program that helps guide care for millions of patients is flawed by unintentional racial bias that leads to blacks getting passed over for special care, according to a new study.

The software predicts costs rather than sickness. It is used by U.S. insurers and hospitals to direct higher-cost patients into health care programs designed to help them stay on medications or out of the hospital.

Whites tend to be higher-cost patients even when they're not as sick as blacks. The study found the software regularly suggested letting healthier white patients into health care risk...