An activist investor who has been campaigning for change at Alere Inc sent the company a letter on Monday calling for the health diagnostics and services company to sell three of its businesses, which it believes can yield more than $3 billion in proceeds. Coppersmith Capital Management, which holds a 5.8 percent stake in the company, has been pressuring the company to make changes since last month. The hedge fund has nominated a slate of three directors to Alere's board. The hedge fund sent the letter days after Alere put its own slate of new nominees up for election to its board, replacing all four of the board members who were expected to stand for reelection this year. Coppersmith said in the letter - which has been reviewed by Reuters - that Alere should exit non-core businesses including its health care management business, called Health Information Solutions; its consumer products joint venture with Procter & Gamble ; and, possibly, its toxicology unit.