March 26 (Bloomberg) -- Shares of Beckman Coulter Inc. fell the most in seven months after the company, a maker of laboratory and diagnostic equipment, agreed to buy the test-maker Biosite Inc. for $1.55 billion.

The price of Beckmann Coulter shares dropped by $4.57, or 6.8 percent, to $62.51 at 4:00 p.m. in New York Stock Exchange composite trading. Shares of Biosite gained the most on record.

Beckman Coulter said yesterday it offered $85 a share for Biosite, 53 percent more than the closing price on March 23. The acquisition would make Beckman Coulter a top provider of tests used to diagnose heart disease by checking blood or bodily fluids. At the same time, analysts and ratings services said they were concerned about Beckman Coulter's level of borrowing.

``There are clearly synergies to be gained by Beckman, but the cost of financing the transaction is still an important, unanswered question,'' said Bruce Jackson, an analyst with RBC Capital Markets in Minneapolis, in a note to clients yesterday.

Today's drop for shares of Beckman Coulter, based in Fullerton, California, was the biggest since an 8.8 percent decline on Aug. 2, 2006.

Shares of Biosite, which is based in San Diego, surged $28.42, or 51 percent, to $83.80 at 4:00 p.m. New York time in Nasdaq Stock Market composite trading. Today's price was the highest ever, and the increase was the biggest since the stock went public in 1997, according to data compiled by Bloomberg.

Heart Failure

Beckman Coulter and Biosite started working together four years ago on a test to diagnose the severity of heart failure, a disease in which the heart no longer pumps effectively, Garrett said yesterday. The test, the Triage, finds a marker in the blood that can help diagnose congestive heart failure within 15 minutes.

Beckman Coulter said the acquisition will add an unspecified amount to earnings next year. With the purchase, Beckman Coulter's second in five months, the company will be able to expand global sales of Biosite tests.

``We got favorable borrowing terms, and Biosite is the best company in our industry when it comes to developing new tests and taking advantage of the explosion in the life sciences industry,'' Beckman Coulter's chief executive officer, Scott Garrett, said today in an interview on Bloomberg television.

Standard & Poor's Ratings Services and Fitch Ratings put Beckman Coulter's `BBB' corporate credit on alert for a possible downgrade, citing the leverage required to finance the Biosite purchase.

Lumigen Purchase

In October, Beckman Coulter said it would buy Lumigen Inc., a Southfield, Michigan, maker of chemicals used in diagnostics and scientific research, for $185 million in cash.

Morgan Stanley advised Beckman Coulter on the transaction. Goldman Sachs Group Inc. advised Biosite. Morgan Stanley and Citigroup Inc. offered financing.

About 85 percent of Biosite's products are sold in the U.S., and its Triage tests are used in more than 70 percent of U.S. hospitals.

Beckman Coulter said 2006 net income jumped 26 percent to $2.9 million, or $2.92 per share. Excluding special items, earnings were per share was $2.88, the company reported last month.

To contact the reporter on this story: Lisa Rapaport in New York at rsimison@bloomberg.net.

Last Updated: March 26, 2007 16:08 EDT