The "minute clinic" has efficiency built into its name, a quick, easy way for people who feel sick -- but not that sick -- to seek medical treatment without the hassle of making a doctor's appointment. Early evidence showed that visits to retail clinics embedded in grocery stores, big box stores and pharmacies cost much less than traditional health care, suggesting they could be a way to cut overall spending.

But a new analysis shows that, paradoxically, the rise of the retail clinic has meant a small but significant rise in health care spending. Retail clinics accounted for an additional $14 per person per year, according to a Health Affairs study that examined how people insured by Aetna in 22 cities between 2010 and 2012 used health care. That's because more than half of the visits to retail clinics for sinus infections or other relatively minor illnesses were driven new utilization -- in other words, visits that wouldn't have happened if the clinics didn't exist.

"The major point of this paper is that a lot of people have said, 'Hey, they’re 30 to 40 percent cheaper -- let’s get people to go to retail clinics and we’re going to save a lot of money for our health care system,'" said Ateev Mehrotra, an associate professor of health care policy at Harvard Medical School, who led the study. "That’s the logic, and that logic is missing a key point: when you make something more convenient, people are going to use more of it."

In a classic case of "if you build it, they will come," more than 6 million patient visits occur at the 2,000 clinics embedded in pharmacies, grocery stores and big box retailers each year, and the trend looks to be on the rise.

Mehrotra's own work has shown how much money can be saved in retail clinics compared with conventional health care settings. For three common conditions -- earache, sore throat and urinary tract infections -- a visit cost on average $110 at a minute clinic. Treatment for the same conditions cost $166 in a doctor's office, $156 in an urgent care center and $570 in an emergency room.

That is good news, but what it fails to measure is whether lowering the bar to access simply means more people simply seek care. The study found that 58 percent of retail clinic visits for 11 conditions were "new utilization." That means this isn't a shifting of care from a more expensive location, but simply people taking advantage of the convenience of quick, cheap, on-demand care.

What those numbers can't explain is crucial: whether that increased use of health care makes people healthier and avoids long-term costly care.

"If I showed that retail clinics were driving up the number of people who got flu vaccines or were getting care for heart failure or diabetes or blood pressure, I think we’d be standing on our chairs and clapping. Too few people get care for those things," Mehrotra said. But many of the conditions that drive people to seek care at retail clinics include symptoms that tend to resolve on their own. That leaves open the question of the extent to which retail clinics have longer-term effects on health or really avoids other health care spending.

In response to the study, CVS Health spokeswoman Amy Lanctot sent a statement critiquing the study, pointing out that it used five-year-old data and did not include preventive care that makes up 40 percent of retail clinic care, which could hold down health spending. Half of CVS' MinuteClinic patients do not have a primary care doctor, meaning they serve a crucial function due to a shortage of primary care doctors.

"The authors’ conclusion that this represents new care and new costs is a step backwards, and fails to recognize that reaching this underserved population is not excess utilization; rather it is the underlying objective of many health system innovations," the statement said. "A patient with the flu who does not have a physician can get convenient, inexpensive care at a retail clinic, even on the weekend, before their condition worsens.  This care can prevent a costly hospitalization, improving health and saving resources that are not measured by this limited study design."

Walgreens released a statement saying that 40 percent of patients who visit its Healthcare Clinics say they would either go somewhere more expensive for care or not get care at all if it weren't for the in-store clinics.

Walmart also pushed back against the study. Spokeswoman Molly Blakeman described a recent patient who had her blood pressure taken at its Walmart Care Clinic and was sent to the hospital because it was high.

"Soon thereafter, her daughter called to report that had it not been for the blood pressure screening and the immediate action taken by the nurse practitioner, it is likely the mother would have had a heart attack or stroke within hours," Blakeman wrote.

Mehrtora said he did not think people were seeking frivolous care at retail clinics or that they don't serve an important role. And there's a larger point: even if the care people receive at retail clinics is for conditions that are unlikely to play into people's long-term health, the care could still have value to individual people.

But if the health care system -- essentially, all of us, through the premiums and deductibles we pay -- are footing the bill for minute clinic visits, the assumption that it will lead to health care savings needs closer scrutiny.