Niche healthcare stock IDEXX Laboratories (NASDAQ: IDXX) has landed in a group that is far from niche: the S&P 500 stock index. It replaced fellow healthcare enterprise St. Jude Medical (NYSE: STJ) at the close of trading on Wednesday.

St. Jude Medical is exiting the index because it will no longer be an independent, publicly traded company. It is in the process of being acquired by big peer Abbott Laboratories in a cash-and-stock deal that was anticipated to close on Wednesday. St. Jude Medical agreed to the buyout  last April; the transaction was valued at roughly $25 billion at the time.

IDEXX Laboratories had been in the S&P MidCap 400 index prior to its advancement. Taking its place on that index is chemical company Chemours (NYSE: CC), a recent spinoff of industry giant DuPont. Chemours had been a component of the S&P SmallCap 600 index. Chemours' slot on the latter will be filled by popular burger restaurant chain operator Shake Shack.

IDEXX Laboratories specializes in animal health diagnostic products -- essentially, it's market is a niche within a niche in the healthcare industry. It's also a consistently profitable company and, not coincidentally, a popular stock. Its shares have risen by nearly 58% over the past year. Across that stretch of time, its market capitalization has grown to over $23 billion.

Although joining the S&P 500 won't change the fundamental investing thesis for IDEXX Laboratories, it will raise the company's profile considerably. The S&P 500 is considered one of the key stock indexes, if not the key index, on the U.S. market.

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Eric Volkman has no position in any stocks mentioned.

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