Patients are waiting an average of 18 days to schedule an appointment for a doctor, according to a study of appointments for commonly used specialty physicians in 15 major U.S. cities. The survey by physician staffing and consulting firm Merritt Hawkins comes as a doctor shortage looms as more patients seek medical care under the Affordable Care Act. The health law is bringing millions more Americans health benefits and therefore the ability to pay for a visit to the doctor’s office.

The longest wait to see a doctor was in Boston where the average wait was 45.5 days to schedule an appointment with a family physician, dermatologist, cardiologist, orthopedic surgeon or obstetrician/gynecologist. The survey came from a sampling late last year of nearly 1,400 medical offices across the country.

“In the next two to three years, can we keep a bad situation from getting worse?” asked Travis Singleton, senior vice president at Merritt Hawkins, a subsidiary of AMN Healthcare (AMN). ”Everything will tell you it’s going to get worse and not better.”

The increase in doctor wait times to this point isn’t completely related to the health law. The improving economy is also driving more Americans to the doctor’s office. In recent years, data has showed slow growth in visits to doctor’s office during a period of high unemployment as well as the trend for insurance companies and employers to increase co-payments and deductibles.

“Finding a physician who can see you today, or three weeks from today, can be a challenge, even in urban areas where there is a high ratio of physicians per population,” said Mark Smith, president of Merritt Hawkins. “The demand for doctors is simply outstripping the supply.”

When health care coverage is expanded and there is more access to physicians, wait times rise.

Take Boston, which has a high number of “physicians per capita,” Singleton said. “Yet they still have the longest waits for appointments.”

Massachusetts has had broad health care coverage for most of its residents for several years now and the state’s law was the model for the Affordable Care Act.

“People are accessing the system (in Massachusetts) at greater and greater levels,” Singleton added.

There is, however, good news for appointment times as health care reimbursement moves away from fee-for-service medicine to value-based care that emphasizes the use of accountable care organizations and patient-centered medical homes.

In ACOs and other models, doctors are handing off more responsibilities to physician assistants and nurse practitioners with the physician as more of a quarterback of sorts.

Medicare and most private insurers like those operated by Aetna, Cigna, Humana, UnitedHealth and most Blue Cross and Blue Shield plans are linking with ACOs, which push high quality, less expensive care rather than today’s payment system that often leads to excessive care by paying for each treatment or procedure that isn’t always better.

The providers in an ACO are responsible for managing the care of the health plan enrollees and are financially rewarded if the enrollees, or patients, stay out of the more expensive hospital.

“We are much better at managing the health care system and using nonphysicians,” Singleton said. “We are much better at using nurse practitioners and physician assistants.”

Cities with the Longest Doctor's Appointment Wait Times

No. 1-Boston- 45.4 minutes

No. 2-Denver- 23.6 minutes

No. 3-Philadelphia- 20.6 minutes

No. 4-Portland- 19.4 minutes

No. 5-Minneapolis- 19.2 minutes

No. 6-Detroit (tie)- 17.8 minutes

No. 6-Washington, DC (tie)- 17.8 minutes

No. 7-New York, NY- 16.8 minutes

No. 8-San Diego- 16.2 minutes

No. 9-Seattle- 16 minutes