Investors are eyeing an opportunity as companies find new ways to provide health insurance to their workers and retirees, but picking the next stocks to pop in that trend is easier said than done.
The potential of the trend toward private health exchanges was underscored this week by an IPO that saw its shares go through the roof, and disclosures that yet another large company was moving workers to such an exchange.
Benefitfocus, a newly public software solutions company specializing in benefits and private exchange platforms, saw its share price explode Wednesday from an opening of $26.50 to a close of $53.55—a 102 percent spike—in its first day of trading on Nasdaq.
That dramatic debut came on the heels of the day's earlier news that retailer Walgreen will send up to 160,000 active employees into a private health exchange run by Aon—which has signed up 18 employers this year.
Two weeks ago, news broke that IBM was shifting 110,000 retirees into a Medicare private exchange run by Towers Watson's ExtendHealth division, which already has about 300 companies as clients. Towers Watson's exchange primarily handles retirees but expects to soon sign up several big companies for active workers. Days later, Time Warner revealed it also would direct retirees to an exchange to get health coverage.
Private health exchanges offer multiple competing insurance plans, at different levels of premium and out-of-pocket costs, to workers, who usually are given cash by their employer to offset the purchase price. The online exchanges give employees increased options to meet their individual insurance needs and shift some of the cost and administrative burden from employers to workers.
(Read more: Private health exchanges set to explode)
For investors, "It's a bit too early to know who the winners are going to be," said Rich Birhanzel, managing director of Accenture's health administration division.
Birhanzel was referring to big professional services companies, such as Towers Watson and Aon Hewitt. These types of companies run their own private health exchanges. Birhanzel sees them as the first category of possible buys for investors, who could find it even more difficult to pick winners and losers among other companies tied to the trend.
"The second category is in the space of the technology providers, those that are providing solution platforms in this space," Birhanzel said. "The third category is the [insurance] carriers that get it right, that are effective in putting the right products on the shelf."
There is widespread expectation that private health exchanges will significantly increase enrollment from their current level of 1 million in the next five years. Booz & Co. predicts a maximum of 20 million people in private exchanges by 2018, Accenture sees as many as 40 million, and others expect private exchanges to become the dominant insurance scheme for 150 million or so workers now in company plans.
"We've just concluded the first inning of the ball game with retired workers," said Towers Watson's ExtendHealth leader Bryce Williams. "With active employees, the National Anthem has just been sung—we're at the beginning of the ball game."
Booz partner Ashish Kaura agrees.
But, "if you want to go along for the ride, Kaura said, one option would be to look at stock in large employers, ones with many thousands of workers, who "if they go on a private exchange, they might see 'x' billion dollars in savings" in health-care costs.
(Read more: Companies eyeing private health exchanges as Obamacare looms)
Last year, when Towers Watson bought the ExtendHealth exchange for $435 million, Psilos Group Managers, a health-care investment firm, realized a 10.7-to-1 return on its investment in ExtendHealth.
Duplicating that return might be tough for public stock investors. But Psilos co-founder Al Waxman said they could do worse than buy stock of big benefits consultants like Towers Watson, Aon and others.
"They're all rushing to get into this business," Waxman said.
Waxman noted that those companies already have significant, long-standing relationships with companies that might shift their workers to private exchanges.
"These people can control a lot of lives in the corporate world," Waxman said.
Steve Kraus, vice president of Bessemer Venture Partners, which has an undisclosed stake in private-exchange operator Liazon, said he expects some companies whose sole business is operating private exchanges to go public over the next couple of years. Liazon, whose Bright Choices Exchange has employees from more than 2,300 companies enrolled, has not announced any plan to go public.
Kraus also said, "I actually don't rule out a surprise entry" into the private-exchange business.
"Think about some of the large marketplaces based in Silicon Valley that are all about consumer service. This is just another marketplace," Kraus said.
He said companies that already sell "books, electronics, food on-line," could view private exchange insurance as big potential opportunity that would leverage their existing skills of offering customers products with competing price points in an attractive, easy-to-navigate Web platform.
"I know that some of the big retailers, I've heard that Costco, Wal-Mart, Target, they've all looked at the health-care space," Kraus said.
Another possible opportunity for investors from the private-exchange trend is in selling short the stocks of big insurance companies, said Richard Evans, health-care analyst for Sector and Sovereign Research.
Evans noted that giant insurers like Cigna, Aetna, WellPoint and UnitedHealth "have a lock on these big employers" who offer workers health coverage. As a rule, employers will offer plans from just one insurer to workers.
"If the big employers throw all their beneficiaries in the exchanges, then these beneficiaries are a jump ball now," Evans said, noting that the insurers would then have to compete on price for the workers.
That would be likely to drive premiums prices—and insurers' profits—down, Evans said.
(Read more: The "Expedia" of health care: start-up rides Obamacare wave)
Another stiff hit to insurers' bottom line would come from the tendency of purchases in private health exchanges to buy plans with significantly lower premium prices—and higher deductibles and co-pays—than what their current company-offered plans cost, Evans said.
But in the long term, Evans said, one or more of the big insurance companies could look at the writing on the wall and realize that they need to get in the private exchange business themselves to offset the competition.
"These guys have a system advantage that would be staggeringly difficult for anyone to overcome," Evans said.
"If I had to guess right now, it'd be Cigna" that would be first to get into the business of operating a private exchange. "UnitedHealth would be second," with Aetna and Wellpoint less likely to jump quickly into the sector, he said.
—By CNBC's Dan Mangan. Follow him on Twitter @_DanMangan.