The Omaha-based conglomerate bought more than 5 million shares in the healthcare firm for a stake worth about $1.6 billion at the end of June.

Shares of UnitedHealth Group surged more than 12% in premarket trading today after Warren Buffett's Berkshire Hathaway revealed a new investment in the US health insurer.

"This UnitedHealth analysis perfectly demonstrates the power of leading indicators over reactive decision-making," said Lane Mendelsohn, President of Vantagepoint A.I..