The health insurance world is abuzz with talk of mergers these day, but UnitedHealth Group executives on Thursday were having none of it.

Earlier this month, health insurer Aetna announced a $37 billion deal to purchase Humana, which rivals United in the Medicare market. Meanwhile, Indianapolis-based Anthem has proposed buying Cigna.

There have been rumors about United getting in on the action, too, but during a conference call to discuss strong second quarter results, company officials steered clear of the chatter.

"Certainly, we all recognize this market space has been exceptionally active this quarter," said Stephen Hemsley, the company's chief executive, during a conference call with investors. "But beyond that observation, we do not believe it is our place to comment on market specific activities or hypothetical implications."

An Anthem/Cigna deal could effect UnitedHealth's growing business in pharmaceutical benefits management (PBM), analysts say, because Anthem uses St. Louis-based Express Scripts as its PBM. Cigna, meanwhile, is a key customer for a PBM called Catamaran Corp., an Illinois-based firm that UnitedHealth is in the process of buying in a $12.8 billion deal.

Analysts aren't sure whether ­Catamaran could retain the Cigna business if an Anthem merger goes forward. Big membership numbers can be important for PBMs, because they can provide leverage in negotiating price discounts from drug ­manufacturers.

Asked on Thursday about the prospect of Catamaran losing large customers by way of mergers, UnitedHealth officials didn't say much.

"We are intensely focused on serving all of our customers, and serving the expectations of the Catamaran customers, for sure," Hemsley said. "There's significant value coming their way from this combination, and we think that that is going to be compelling."

UnitedHealth is the nation's largest health insurance company. At the end of June, about 45.9 million people were buying health insurance from the company.

If the Aetna/Humana merger goes through, United would still have a bigger membership tally, said Ana Gupte, an analyst with Leerink. A merger between Anthem and Cigna would create a bigger company in terms of membership, Gupte said, but that doesn't necessarily spell trouble for United.

Insurers usually compete in local markets, Gupte said, so comparing tallies of national membership isn't the best way to analyze a ­company's strength.

If United stands apart while the other four big national carriers merge, is that a problem?

"They're pretty strong on their own, so they've already got pretty solid membership," Gupte said. "I think if they can pick up, through some tuck-in acquisitions, some more membership in targeted places, they'd be fine."

"If any of the other players is left behind alone, it's harder because they don't have the scale and diversification that United does," she said.

Plus, UnitedHealth Group will continue to be the largest company by revenue thanks to its Optum health services business, which has been the bigger growth driver, said Sheryl Skolnick, an analyst with Mizuho Securities.

"Optum is again the star," she wrote in a research note about the second quarter results. "Pretty soon [UnitedHealthcare] will be the ­minority business."

United's headquarters operation in the Twin Cities — it employs about 14,000 people in Minnesota — provides one of the few links between the state and the national talk about health insurance mergers. Minnesota's market is dominated by local nonprofits, where there's been no public discussion of mergers.

Overall, UnitedHealth Group on Thursday posted second quarter earnings of $1.58 billion on revenue of $36.3 billion. A year ago, UnitedHealth saw quarterly earnings of $1.41 billion on about $32.6 billion in revenue.

Earnings per share grew to $1.64, which was better than the $1.59 per share expected among analysts surveyed by Thomson Reuters.

The Catamaran deal is expected to close this month, and UnitedHealth now expects total 2015 revenue of approximately $154 billion as a result — an increase of $11 billion from the previous outlook.

For the year, UnitedHealth now expects earnings in a range of $6.25 to $6.35 per share, up from the previous outlook of $6.15 to $6.30 per share.

While health insurance revenue grew by about 10 percent for the second quarter, the company's Optum division for health services grew sales at a faster 16 percent rate.

Shares of the health insurance company's stock were off in early trading Thursday, amid analyst concerns that medical costs in the quarter might have grown at a greater than expected rate. Citing this, Goldman Sachs analyst Matthew Borsch wrote in a research note: "We expect the stock may be weak on these results."

But company officials said Thursday they didn't see any medical cost surprises during the quarter. The stock closed at $124.93, down less than 1 percent for the day.

Twitter: @chrissnowbeck