Some doctors, burned by low reimbursements, have stopped testing for the virus.

Across the United States, some doctors are seeing reimbursement rates so low that they do not cover the cost of the test supplies, jeopardizing access to a tool experts see as crucial to stopping the virus’s spread.

With new variants of the coronavirus emerging, experts say testing will be crucial to containing the pandemic’s spread. But the low fees have led some doctors to stop testing certain patients, or forgo testing altogether.

The problem of low reimbursement rates appears to be most common with pediatricians using in-office rapid testing.

“We are not doing Covid testing because we cannot afford to take the financial hit in the middle of the pandemic,” said Dr. Suzanne Berman, a pediatrician in Crossville, Tenn. Her clinic serves a low-income Appalachian community where the coronavirus is spreading rapidly, and 17 percent of tests are coming back positive as of this week.

Rapid in-office tests are less sensitive than those sent off to a lab, which means they miss some positive cases. Researchers are still learning about the efficacy of these tests in children. Still, infectious disease experts say that fast turnaround tests are important in controlling the pandemic, particularly in areas where other types of testing are less available.

Across the United States, multiple doctors identified UnitedHealthcare and certain state Medicaid plans as the ones that routinely pay test rates that do not cover the cost of supplies.

Medicaid and Medicare often pay lower prices than private insurers do. But the reimbursements from a large private insurer like UnitedHealthcare came as a shock to doctors.

A spokesman, Matthew Wiggin, said that UnitedHealthcare was not underpaying for coronavirus testing, and that its rates were consistent with those of other health plans.

“We want to make sure every member has access to testing and encourage any provider with payment questions to contact us so we can resolve their concerns,” he said in a statement.

Doctors who have complained to UnitedHealthcare and other health plans, however, say they’ve been offered little recourse. One was told it wasn’t an issue that any other doctor had raised. Another was directed to find a supplier with a lower price.