WASHINGTON — One in five Americans don’t have access to doctors when they need them due to a shortage of primary care physicians, Sen. Bernie Sanders said Tuesday.

The Senate subcommittee on primary health and aging grappled with ways to solve the problem and more specifically to help 30 million previously uninsured Americans who will receive health care coverage under the Affordable Care Act.

The panel’s hearing Tuesday drew such a large crowd that some members of the public stood just outside the doors, which “tells you how seriously many of us feel about this issue,” Sanders said.

Sanders, a Vermont independent who heads the subcommittee, said America’s shortage of primary care disproportionately affects the elderly, minorities, poor and those who live in rural communities, especially in states like Wyoming and Vermont.

Increased access to primary care physicians, who treat common illnesses and perform routine check-ups, is vital for “better health outcomes and lower health disparities,” Sanders said.

In America, there are about 280 physicians for every 100,000 people, according to Dr. Fitzhugh Mullan, a professor of medicine and health policy at George Washington University. America’s rank among developed countries is middling when it comes to the amount of doctors per capita, but the U.S. is “disproportionately specialist-heavy,” he said.

Part of the problem is a consequence of many new physicians choosing to become specialists in fields like radiology, which yield significantly higher earnings. Of all American physicians today, 70 percent are specialists. In 2011, only 7 percent of medical school graduates went into primary care, Sanders said.

Sanders spoke to the financial issues facing medical school graduates, who carry a median of $160,000 in debt. “If we’re going to attract more young people to become primary care physicians, we must make primary care more financially attractive,” he said.

One way to do so would be through loan forgiveness programs for medical school graduates who pursue careers in primary care, panelists at the hearing said.

“If you have more primary care physicians, research shows that that will produce better health outcomes,” Princeton University economics professor Uwe Reinhardt said. “We economists can convert that to quality-adjusted life years … and put a value on it by asking, ‘By having more physicians in that field, how many quality life years have you produced?’”

Specialists often earn significantly more than primary care physicians, which could translate to as much as $2.8 million more in individual income over a lifetime, Sanders said. Part of the discrepancy in earnings between specialists and primary care physicians can be attributed to the way costs for medical care are decided, a system which should be changed to address the shortage of primary doctors, according to Mullan and Andrew Wilper, acting chief of medicine at the Boise VA hospital.

In dealing with the pay gap, any proposal would have to take in account a board of physicians from the American Medical Association that serves as the predominant medical cost-setting mechanism, according to panelists.

The board, which is called the Specialty Society Relative Value Scale Update Committee (or more commonly, RUC), determines medical reimbursement rates for the Centers for Medicare and Medicaid Services, the largest single-payer system in the United States. In this manner, the RUC basically sets the cost of medical care for the whole system.

Many of the reimbursement codes date back to the 1980s and are ill-equipped to deal with the realities of medical care today, said Wilper. The system often benefits specialists, who are sometimes reimbursed at the same rates for far less time spent with patients, he added.

Policymakers must pay attention to this issue to narrow the pay discrepancy and offer incentives for physicians to work in primary care, Wilper said.

“What you have lurking under this issue is: Do you raise the floor [and increase primary care compensation] or bring the ceiling down [and decrease specialist compensation]?” he said. “It’s a moral argument we need to engage in as a country.”