WESTBROOK — Idexx Laboratories on Wednesday became the only Maine-based company included in Standard & Poor’s 500 Index.

“This recognition is a testament to our growth since our founding on the Portland waterfront 34 years ago,” said Jonathan Ayers, chief executive of the company that’s been based on Eisenhower Drive for more than 25 years, in a Tuesday press release.

Idexx manufactures test kits and devices primarily related to veterinary, livestock and dairy diagnostics, as well as water testing. The company replaced St. Jude Medical on the index, according to an S&P press release.

The S&P 500 is the market indicator most professional investors use to determine how stocks are performing. It encompasses 500 top companies in leading U.S. industries. Many mutual funds use it as the benchmark they measure their own performance against.

The company’s stock (NASDAQ: IDXX) is listed on the S&P Global Industry Classification Standard Health Care Equipment Sub-Industry index. Idexx had been previously listed on the S&P MidCap 400 index.

“It’s an incredible honor for Idexx to be included in the S&P 500, alongside many of the world’s most respected companies,” Ayers said.

Company spokeswoman Robin Woodcock said Idexx now employs 7,000 people globally; 2,300 of them work in Westbrook.

Founded as a private company by Scarborough resident David Shaw, Idexx was first based at 144 Fore St. on Portland’s waterfront. In 1991, the company stock became publicly traded on the NASDAQ exchange. Shortly after that, the company moved to Westbrook. Ayers became CEO in 2002, Woodcock said.

Idexx has long made screening kits for diseases found in pets, including feline HIV, Lyme disease, and canine heartworm. There are also tests for livestock diseases and for equine and poultry health.

Company filings with the U.S. Securities and Exchange Commission show Idexx earned $448 million in the third quarter of 2016, from July 1 through Sept. 30. The third quarter earnings were almost $42 million more than the third quarter in 2015.

For the entire year up to Sept. 30, 2016, the company reported revenues of $1.33 billion, up from the $1.2 billion reported from Jan. 1 to Sept. 30, 2015.

The company share price on Jan. 3 closed at $115.53 per share, and has been as high as $121.77 in the last year.

David Harry can be reached at 781-3661 ext. 110 or dharry@theforecaster.net. Follow him on Twitter: @DavidHarry8.

Westbrook-based Idexx Laboratories is listed on the S&P 500 Index. The company makes testing kits and diagnostic devices for veterinary science and water testing.