Concateno said it would consider its options, including a possible sale of the company, and had appointed UBS as an adviser. The AIM-listed firm did not name the potential bidders.
Its shares rose 9.43 per cent, or 12.7p, to 148p, valuing Concateno at £140m.
The company, which floated in 2005, has become a leader in corporate testing after a string of acquisitions. In December 2006, it bought Altrix for £11.m.
Altrix, based on the Birchwood Science Park, sells drug-testing kits and analyses the results in a laboratory.
Its customers include public sector organisations such as community drug teams and probation services, as well as companies which conduct tests among their staff.
Last last year, Concateno announced plans to shut its lab in Warrington in a savings drive. Concateno was a cash shell until it bought London-based Medscreen, for £30m in November 2006. Last year, it bought Liverpool's CPL, TrichoTech, Euromed and Marconova of Sweden.
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