Walgreen Co. has stretched the reach of its drugstore clinics beyond treating ankle sprains and sinus infections to handling chronic diseases such as diabetes, asthma and high blood pressure.

The company, based in Deerfield, Ill., said Thursday that most of its 370 in-store Take Care Clinics now will diagnose, treat and monitor patients with some chronic conditions that are typically handled by doctors.

These clinics, which are run by nurse practitioners or physician assistants, have grown popular in recent years as a convenient and less expensive way to treat relatively minor illnesses when a patient doesn't have a doctor or if their physician isn't available. But the clinics have been broadening their scope of care: Walgreen's decision follows a move by competitor CVS Caremark Corp. a few years ago to start monitoring chronic conditions at most of its 640 MinuteClinics.

Drugstores say they don't aim to replace doctors, but rather to provide more people with access to health care and to work with physicians as part of a team treating patients. But the move to provide more complex care draws concern from doctors who say that can disrupt their relationships with patients and lead to fragmented care.

Physicians know their patients, and that makes them better suited for doing things like helping someone with diabetes develop an exercise plan, stick with their treatment or learn how to eat better, said Dr. Jeffrey J. Cain, president of the American Academy of Family Physicians, one of the nation's largest medical organizations. And different computer systems can make transferring records between clinics and health care providers a problem, leading to test duplications and gaps in a doctor's knowledge of a patient's care, he said.

"It's not about telling somebody what they have to do, it's helping them make choices in their life to move toward a healthier lifestyle," he said.

Cain compares the clinics to fast-food restaurants, which are good for the occasional meal but not something a person wants to rely on for too much of their diet.

But Walgreen said its expansion into chronic care is based on need. Cases of diseases like diabetes are growing, the U.S. population aging and the health care overhaul will increase coverage to millions of uninsured people next year. And the coverage expansion will arrive as the country struggles with a doctor shortage, Walgreen noted.

Some studies have predicted a shortfall of roughly 40,000 primary care doctors over the next several years.

"If there wasn't a primary care access crisis ... I don't think we'd be expanding our services quite like this," said Dr. Alan E. London, chief medical officer for the Take Care Clinics.

He said nearly half of the patients who receive treatment at Walgreen clinics don't have a primary care doctor or have trouble finding one who accepts the government-funded Medicare or Medicaid covearge.