Some 1,500 lower-income Vineyard residents face the prospect of having to find new health insurance because the Martha’s Vineyard Hospital has determined its current insurer is not directing enough patients to its affiliated hospitals in Boston.

Hospital chief executive officer Timothy Walsh confirmed this week that the hospital intends to drop its contractual arrangement with the Boston Medical Center (BMC) HealthNet program and enter into a new one with Network Health. He said the hospital plans to allow its contractual arrangement with BMC to lapse, and is in negotiation with the other provider.

The hospital has made no public announcement of the move, but some Island doctors have been informed and have in turn begun informing patients that their Boston Medical Center HealthNet coverage will not be recognized after the start of July.

The change, if it proceeds — and Mr. Walsh left little doubt that it would — will mean the 1,500-odd people who now have coverage through BMC will either have to go off-Island for care after July 1, or find a new insurer which operates here.

To date, Network Health has been the only other provider of this type of care.

The change being proposed by the hospital would affect the least privileged, and in some cases the people least equipped to go elsewhere for treatment or to negotiate the bureaucratic red tape of changing insurers — those covered under the Commonwealth Care scheme.

In 2006 Massachusetts adopted a mandatory health insurance law, seen as a first step toward universal health care in the commonwealth. A state agency named Commonwealth Connector manages two programs for people who do not have private health insurance through traditional means. Commonwealth Care is the program that connects people with low incomes to health coverage.

Commonwealth Care is offered to people earning up to 300 per cent of federal poverty level income, and who are not offered employer-sponsored insurance.

For an individual, that is $32,508 per year. For a family of four it’s $66,168.

For people earning up to half that amount — $16,260 for a single person, $33,084 for a family of four — coverage is free. For the other group premiums are charged on a sliding scale.

Statewide, the Commonwealth Care program is offered through four insurance carriers referred to as Medicaid managed care organizations. None offers coverage in all parts of the state.

Sarah Kuh, director of the Vineyard Health Care Access Program, said her program has helped enroll some 800 Island people with Boston Medical Center Healthnet.

On Tuesday Ms. Kuh said her organization also had heard word of pending changes, but had received few details from the hospital.

“We’re in the middle of trying to get all this clarified so we can work with our clients, so they understand what’s going on,” she said.

A change in the hospital’s insurance contracts affects not only patient access to care at the hospital, she said, but also to other medical providers on the Island.

“The way it works is that a hospital is a sort of an anchor for a service area for each of these health plans.

“If there’s a health plan that doesn’t have a contract with a hospital, especially for an Island, it’s not much good to the members,” Ms. Kuh said. She continued:

“And there are other providers outside the hospital also affected by these changes, like mental health care providers, primary health care providers, and so on.

“If the plan disappears from the service area, people with that plan will no longer be able to get care from someone in private practice, either.”

Ms. Kuh said that while Network Health is the only other provider on the Island for Commonwealth Care, she had been told that another provider, Neighborhood Health Plan, was in the process of setting up here.

On Wednesday Mr. Walsh said the move was driven by the fact that Boston Medical Center had no contractual arrangement with Massachusetts General or Brigham and Women’s Hospital in Boston.

Two years ago, the Vineyard hospital, after 80 years of independent operation, was acquired by Partners Health Care, the group that owns Massachusetts General Hospital and Brigham and Women’s. Partners is by far the largest provider of medical services in Massachusetts.

“We originally signed with BMC about 18 months ago, and what we’re finding is they don’t have an extensive set of contracts with all the providers up in Boston, and in particular with Brigham and Women’s and Partners,” Mr. Walsh said, adding:

“Our referral network from here generally goes in that direction.

“That’s why we’re going to switch and why we’re in the process of signing with Network Health . . . [which] has contracts. It has a more extensive array of hospitals available.”

As things currently stand, Mr. Walsh said, “Every time we want to move a patient to Boston, they have to go to BMC. They can’t go to Mass General if they’re in the BMC HealthNet.

“Providers will also swing over to Network Health too, so everything is covered by Network Health. That’s probably 16 doctors, mostly primary care and some surgeons and others.”

He said Mass General had long been in talks with BMC toward a potential contract, but the talks had come to nothing.

Contacted by the Gazette his week, BMC put out the following statement:

“BMC HealthNet Plan has had a relationship with Martha’s Vineyard Hospital since June 2006.

“Since that time Martha’s Vineyard Hospital has provided care to BMC HealthNet Plan members living on and visiting the Island. This agreement is still in place and Martha’s Vineyard Hospital continues to see BMC HealthNet Plan members.

“The health plan’s current contract with Martha’s Vineyard Hospital runs through July 1, 2009. BMC HealthNet Plan is in discussions with Partners Healthcare, the parent company of Martha’s Vineyard Hospital, and we look forward to our continued relationship.”

Later, after hearing the statement from BMC, Mr. Walsh said he still hoped an agreement could be struck.

“It’s hard to tell, but they’ve been talking for a while,” he said.

Meanwhile 1,500 Islanders are left facing the probability that, come July, they will need to switch their current health insurance plan.