Roughly 21,000 people in Hawaii who were previously covered under Medicaid will need to buy their own health insurance once President Barack Obama’s sweeping federal health care overhaul takes effect next year, the chief executive of the Hawaii Primary Care Association told a state Senate committee today.

Robert Hirokawa, of the Hawaii Primary Care Association, said during an informational briefing of the Senate Health Committee that the group represents a so-called “gray” zone that lawmakers should consider as they approach implementing the law.

The gap represents people whose income ranges from roughly 38 percent above federal poverty levels to two times the poverty line.

Hirokawa said single people earning $18,000 per year — 138 percent of federal poverty levels — can expect to pay $75 per month on insurance premiums. Those making twice the poverty level, or $26,000 per year, can expect to pay $194 per month.

The association represents roughly three dozen clinics throughout the islands that provide primary care for patients. The nonprofit clinics are considered an important part of the health care system because patients can be treated at costs far lower than emergency rooms.

Sen. Josh Green, an emergency room doctor who represents the west side of the Big Island, said the state needs to help close the gaps.

He said he saw an 8-year-old patient early today with a low-grade fever who clearly should have used a health clinic rather than pay $400 for an emergency room visit.

He said in addition to figuring out coverage details, the state needs to better steer people toward cheaper clinics rather than their more expensive neighbors.

“You know you have my support to expand services and to make sure the money goes to whatever possible health service,” Green said.

Officials from several clinics statewide expressed worries that people will have to choose between paying for health care and paying for other essentials like food, utilities or gas to get to work. They told Green and state Sen. Rosalyn Baker that if people choose not to buy insurance, the state will see more emergency room visits.