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'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.

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.