RETAIL MEDICAL CLINICS and emergency care centers are growing at breakneck speed in Massachusetts, a trend that suggests strong demand for the lower-cost alternatives to standard outpatient and hospital emergency services.

The number of urgent care centers increased eight-fold from 18 centers in 2010 to 145 at the end of 2017, according to a report issued on Wednesday by the Massachusetts Health Policy Commission. The number of retail clinics in the state nearly tripled, from 20 in 2010 to 57 in 2018. Growth of the alternative providers was particularly strong in the Springfield and Worcester areas as well as in communities outside Boston.

The commission found “staggering differences” in costs of visits to urgent care centers and retail clinics compared with hospital emergency departments. The average emergency room visit costs just under $900, with an average patient copayment of $118, while the average urgent care center visit costs $149, with a patient copay of $33. For retail clinics, the study found that the average cost of a visit was $69, with an average copay of $20.

The report pointed to one analysis that suggested 27 percent of current visits to emergency departments could be safely handled at urgent care centers, while 13 percent of current emergency room visits could be safely handled at retail clinics.

Urgent care centers generally include physicians on site, have x-ray services, and can handle more serious cases, including bone fractures. Retail clinics are usually staffed by nurse practitioners and handle more routine limited care, including vaccinations and upper-respiratory and sinus infections.

Nearly one in five retail clinic visits in the study was for a sore throat, or acute pharyngitis, with acute sinusitis responsible for another 11 percent of visits.

Urgent care centers were defined as clinics that see patients on a walk-in basis without appointments and are open beyond standard weekday business hours. Retail clinics have a special licensing by the state. At present, CVS Minute Clinics are the only retail clinics operating in the state.

A 2016 report from the commission found that proximity to a retail clinic was associated a 3 percent reduction in avoidable emergency room visits. The report found a smaller reduction in emergency room visits in areas with urgent care centers. That report noted that Massachusetts had the 13th highest rate of emergency room utilization in the country.

There are some striking patterns in the location and ownership of the clinics.

The majority of both types of sites are located in higher-income areas of the state, with 58 percent of urgent care centers in ZIP codes with above-median income and 72 percent of retail clinics sited these higher-income locations.

While most urgent care centers were affiliated with hospitals in 2010, 61 percent of the centers are now part of non-hospital-based chains. Partners HealthCare, the state’s largest health care provider, owns the largest number of urgent care centers among hospital systems with 16 clinics. Southcoast Health, Steward Health Care, and Wellforce Care Plan each own five.

“Urgent care centers and retail clinics have the potential to increase timely and convenient access to low-cost, high-quality care for patients in the Commonwealth, including by reducing avoidable ED visits,” David Seltz, the commission’s executive director, said. But he cautioned that there is still much more to learn about the factors driving the huge growth of the sites, including “their role in enhancing access for underserved populations, and how they participate in care coordination efforts across the broader health care system.”

The Massachusetts Association of Health Plans, which represents 16 insurers covering 2.6 million state residents, said it had not yet reviewed the study, but sounded a generally positive note about new approaches that can deliver care more efficiently. “While we can’t comment on specific details of the report, our members support innovative ways to deliver high quality health care at lower costs,” said Lora Pellegrini, the organization’s president and CEO, in a statement.

The Health Policy Commission report did not attempt to compare the quality of care provided at traditional emergency room and outpatient sites and the new urgent care and retail clinics.

One analysis published last month in JAMA Internal Medicine looked at antibiotic prescribing patterns across the four types of sites, and suggested that urgent care centers may be particularly responsible for overprescribing such drugs. Overprescribing of antibiotics is a major concern as it contributes to antibiotic resistance and can itself be the cause of infections.

According to the report, which was based on a national sample of claims data, antibiotic prescribing for “antibiotic-inappropriate respiratory diagnoses” was highest among urgent care clinics (45.7 percent), followed by traditional emergency departments (24.6 percent), traditional medical offices (17.0 percent), and retail clinics (14.4 percent).