The big selling point of the Affordable Care Act — "Obamacare" to you and I — has been the extension of health-plan coverage to uninsured Americans. The implicit promise was that extending coverage would extend actual care. But yet another study suggests that these new medical customers, many of whom would be accommodated by expanding Medicaid, may not be able to find physicians willing to take them on.

Published October 12 in the American Journal of Medical Quality, the study with the patience-trying title, "Characteristics of Primary Care Safety-Net Providers and Their Quality Improvement Attitudes and Activities: Results of a National Survey of Physician Professionalism" surveyed "safety-net" physicians, so-called because they handle the bulk of uninsured and Medicaid patients, What the authors found is that these health-care providers are already reaching their limits even before expansion takes place.

The full text of the report is behind a paid firewall, but a handy press release about the study from Massachusetts General Hospital hits the high points:

The authors note that the concentration of care for Medicaid and uninsured patients among a limited number of safety-net physicians and the fact that 28 and 39 percent, respectively, of those physicians are not accepting new Medicaid and uninsured patients indicate that the current health care safety net may have reached its capacity. In addition, they note, safety-net physicians' interest in quality improvement and attention to health care disparities suggests that reported differences in the quality of care they provide probably reflect limited resources available to their practices or barriers to care within the local communities.

The authors of the study draw logical inferences for the expansion of demand for safety-net physicians — and even for insured patients who may already be running into difficulties finding doctors as some physicians become demoralized and even cut back or leave the field.

"This study raises very serious concerns about the willingness and ability of primary care providers to cope with the increased demand for services that will result from the ACA," says Eric G. Campbell, PhD, of the Mongan Institute, senior author of the report to be published in the American Journal of Medical Quality. "Even with insurance, it appears that many patients may find it challenging to find a physician to provide them with primary care services."

It's possible that alternative providers, such as nurse practitioners could help fill in the gap, especially on day-to-day care. But state-level licensing laws have stood in the way of exactly that for decades. Reports Stateline.org:

A 2010 Institute of Medicine report, "The Future of Nursing," cited nearly 50 years of academic studies and patient surveys in concluding that primary care provided by nurse practitioners has been as safe and effective as care provided by doctors. But efforts to change "scope of practice" laws to give nurse practitioners more independence have run into stiff opposition. Organized physician groups, which hold sway in most legislatures, are reluctant to cede professional turf to nurses. Arguing that nurse practitioners lack the necessary level of medical training, they insist that it is unsafe for patients to be treated by nurse practitioners without a doctor's supervision.

So, if you have a medical provider you like, I recommend that you cling tight and hang on for the ride. The next few years should be interesting.