DaVita shares tumbled after issuing a weak outlook amid rising care costs, while big investor Berkshire offloaded some shares in a preplanned agreement.

Warren Buffett is arguably the world’s most famous investor, and his investment moves are closely followed. Each quarter, the company he runs, Berkshire Hathaway, discloses its current holdings to shareholders.

Warren Buffett's Berkshire Hathaway said on Thursday night it sold 203,091 shares of DaVita, reducing its holdings in the kidney dialysis services provider to about 35.89 million shares, a 45% stake worth nearly $6.