Charter Internal Medicine, a 9,000-patient primary care medical office in Howard County, has announced that it is reversing plans to cease accepting health insurance and switch to a retainer-style practice next month after state regulators expressed concern over whether such operations should be classified as insurance carriers. In October, the five-physician practice informed patients of the planned move to "retainer-based primary care," a model under which patients would be charged a flat fee of $2,000 a year. The practice would trim the number of patients significantly and would no longer accept private insurance or Medicare. Because Columbia-based Charter is one of the largest internal medicine practices in the county, public health officials and residents worried that the switch would leave thousands of patients without a primary care doctor. The Maryland Insurance Administration held a public hearing Friday to receive testimony regarding whether "concierge" care - also known as "boutique" or "retainer" medicine - should be considered a form of health insurance. Under that model, physicians charge patients an annual fee, typically $1,500 to $2,000, for a set of preventive-care services that often includes unlimited doctor visits and an annual physical. "After we initially decided to switch to the retainer-based medical practice model, both county and state officials have, for the first time, expressed interest in exploring whether or not this model is subject to additional regulations," Charter wrote in a letter to patients that was posted on its Web site. "We feel it would be imprudent to proceed with a practice change until our state government provides clearer direction." Charter did not return calls seeking comment.