Key Takeaways Shares of UnitedHealth Group sank Friday following a report that the U.S. Department of Justice is investigating the company's diagnosing practices.The Wall Street Journal reported that the DOJ is probing whether the company tends to over-diagnose conditions that can earn larger Medicare Advantage payouts.

The Justice Department is probing diagnoses and practices that triggered extra payments to UnitedHealth’s Medicare Advantage plans, people familiar with the matter say.