Laboratory equipment company Thermo Fisher Scientific Inc agreed to acquire private-equity owned Phadia, maker of allergy and autoimmune tests, for about $3.5 billion to expand in specialty diagnostics.

Thermo said on Thursday that the deal to buy Sweden-based Phadia from European private equity firm Cinven would immediately add to earnings. The deal is expected to be completed in the fourth quarter and add 26 to 30 cents per share to 2012 earnings.