Vitals, one of several sites trying to be the "Yelp for doctors," has raised $22 million in a Series C round of funding. The round, which brings the company's total amount raised to $45 million, included Cardinal Partners, Piper Jaffray, Milestone Venture Partners and Greycroft, among others.

Since launching in 2007, the site, which says it serves 13 million people monthly through its consumer site and white label platform, has provided patients with an online service for looking up information and reviews about doctors across the country. With the new funding, Vitals said it plans to develop additional tools that enable patients to access health care information. For example, it intends to help consumers figure out the cost of their health care and make decisions regarding health insurance.

Given growing competition in the online doctor finder space, it's not surprising that Vitals wants to bulk up on its services.  ZocDoc and Healthgrades have long enabled patients to look up reviews and information on doctors. And, in the past few months, electronic health records company Practice Fusion and physician social network Doximity have also launched consumer-facing sites for finding doctors. Some, like ZocDoc and Practice Fusion's Patient Fusion, also enable patients to book appointments with doctors online. But, for the most part, they all exist to give patients more information about potential health care providers.

Even though services for reading and writing doctor reviews continue to proliferate, studies show that most patients ignore them. An April report from PricewaterhouseCoopers found that 48 percent of 1,000 individuals surveyed said they read health care reviews online, while just 24 percent have written a review. An earlier study from the Pew Internet and American Life Project released even lower numbers. According to Pew, just one in five Americans has consulted online reviews for treatments or drugs, doctors, or other providers.  And just three to four percent have posted reviews of their own.

Still, as health care costs rise, health insurance exchanges emerge and Americans find themselves on the hook for more of their health expenses, the hope among many in the industry is that consumers will become savvier about their health-related purchasing decisions and increasingly turn to pro-transparency tools.