For many patients, it has become a routine part of the medical process: Get a diagnosis or treatment plan and then seek a second opinion.

A growing number of online services are offering second opinions and some are seeing increasing patient demand for a second set of eyes.

Some of the services are sponsored by established medical centers, including Massachusetts General Hospital and Cleveland Clinic. Others are independent businesses that work with specialists on a consulting basis. Employers increasingly are contracting with such services, and insurance companies at times require patients to get a second opinion, such as for surgery.

Studies show as much as 20 percent of patients seek second medical opinions; in specialties such as oncology, the rate is more than 50 percent. And recent research has found that second opinions often result in different diagnoses or treatments.

Second-opinion services are “one of those areas that is growing fairly quickly,” said Gregory Pauly, chief operating officer of the Massachusetts General Physician Organization at Massachusetts General Hospital. The hospital’s online second-opinion service, which started about eight years ago, handled about 10,000 cases last year compared with fewer than 1,000 five years ago, he estimated. The growing demand for second opinions, which cost between $500 and $5,000 depending on the case, has come from patients, including people from overseas, and companies that are including the service as part of employee benefits, he said.

Dr. Pauly said opinions are most often requested in areas such as cancer, neurosurgery, cardiology and orthopedics.

Patients can request their medical records be sent to an online second-opinion service, which might order additional tests if needed. The services are especially helpful for people who live far from major academic centers that cover a range of physician specialties. Many insurance policies cover in-person second opinions but don’t pay for online services unless they are offered as part of an employee’s health plan.

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