The health clinics in pharmacies and other retail stores may be convenient, but they may also take a bite out of the traditional doctor-patient relationship, a new study suggests.

Retail health clinics operate mainly out of chain pharmacies, but they're also in some grocery stores and "big box" stores like Wal-mart. There are now more than 1,300 retail health clinics nationwide, according to the non-profit RAND Institute. And among Americans with private health insurance, their use rose 10-fold between 2007 and 2009.

"The scope of care is limited," said Dr. Ateev Mehrotra, the senior researcher on the new study, who works at RAND.

The clinics, which are typically staffed by nurse practitioners, offer quick walk-in care for minor health problems, like strep throat, urinary tract infections and ear infections. People can also go there for vaccinations and certain health screenings, like cholesterol and blood pressure checks.

"And retail clinics themselves have expressed that they don't want to replace primary care providers," added Mehrotra, who is also an associate professor at the University of Pittsburgh School of Medicine.

But some doctors' groups are worried the clinics could do just that. And they're concerned, they say, not just because of their own bottom line -- but because people who rely on clinics may miss out on comprehensive health services, and a consistent "medical home."

So for the new study, Mehrotra's team looked at records from more than 127,000 Americans with private health insurance. That included 23,000 people who used a retail clinic for the flu or other short-lived health problem at some point in 2008; the rest had seen their primary care doctor.

The researchers looked at whether the retail-clinic patients were any less likely to visit a primary care doctor for their next minor health complaint over the following year. It turned out that they were.

Overall, they had 40 visits to a primary care doctor per 100 patients, versus 68 visits per 100 among people who'd seen their regular doctor for their last cold or cough.

SIMILAR QUALITY, LOWER COST

In an earlier study, Mehrotra's team found that for sore throats, ear infections and urinary tract infections, retail clinics and primary care doctors provided a similar quality of care. But the clinics did it at a lower cost: the average visit cost $110, versus $166 at doctors' offices.

And in this study, there was no evidence that retail clinics interfered with routine care for one chronic medical condition: People with diabetes who visited a clinic were no less likely to get routine diabetes-related tests, like eye exams and blood-sugar checks, over the next year.

Still, Mehrotra said, there is a push in the U.S. for more people to have a "medical home" -- one provider who knows you and oversees most of your healthcare. That's considered important to improving the quality of Americans' healthcare, including getting people the recommended preventive services.

In the current study, people who visited retail clinics did have less consistency in their care. They were less likely, for example, to see the same provider more than once.

Of course, many people who visit retail clinics do it because they have no regular doctor.

In a past study, Mehrotra found that about two-thirds of clinic patients had no primary care provider. But, he said, that means that one-third did.

"Most of those people go to these clinics for the convenience," Mehrotra noted. If you're sick and can't get an appointment with your regular doctor right away, for instance, a retail clinic might be a good alternative.

But Mehrotra advised making sure your regular doctor gets a record of your care. You can have the retail clinic fax it, or get a printout of your record and send it to your doctor yourself.

"I think this emphasizes the importance of keeping your primary care provider in the loop," Mehrotra said.

The study is published in the Journal of General Internal Medicine.