Beckman Coulter, which develops biomedical tests is to purchase fellow US firm Biosite for $1.55 billion in a deal which will make it the country’s leading provider of immunoassay tests, especially within cardiac diagnostics.

Under the terms of the deal, Beckman will acquire Biosite in a cash tender offer of $85 per share, which represents a 55% premium over the San Diego-based firm’s closing stock price of $55.38 on Friday. The transaction, which is expected to close in the second quarter of 2007 and has already been approved by BioSite’s board, should “immediately accelerate Beckman's revenue growth, improve operating margins and boost earnings in 2008 and beyond,” the companies said.

Beckman’s chief executive, Scott Garrett, said the deal grew out of a relationship the firms have had over the past four years in the area of B-type Natriuretic Peptide, a test that aids in the diagnosis and severity-assessment of cardiac problems.