Conflicting definitions make it difficult to know how much hospitals really spend on caring for uninsured and underinsured patients.

Researchers with the Internal Revenue Service have published that conclusion in a report prepared in an effort to determine how well tax-exempt hospitals are doing at meeting their legal obligations to serve the poor, meet the general medical needs of their communities, and organize public health and health education efforts.

The researchers received with voluntary, unverified survey forms from a non-random sample of 487 hospitals.

Almost all of the hospitals said they provide at least some “uncompensated care,” and only about 10% said they ever refuse to provide care because patients are unable to pay, the IRS researchers report.

Only 4% of hospitals said they require patients to make payment arrangements before receiving emergency care, and 14% said they require patients to make arrangements before receiving inpatient care.

Uncompensated care amounts to an average of 7.44% of the participating hospitals’ revenue, and the hospitals spent an average of $2,510 per patient visit for patients who received uncompensated hospital care, the participating hospitals estimated.

Although public health advocates say about 12% of U.S. residents lack health coverage at some point during the year, only about 7% of the patients who visit the hospitals participating in the IRS survey are completely uninsured, the hospitals told the IRS.

The IRS researchers note that definitions of “uncompensated care” vary widely.

In some cases, for example, hospitals measure the value of care provided for uninsured patients by calculating the difference between what the hospital bills a patient and what the patient actually pays, the researchers report.

In other cases, a hospital may calculate the value of uncompensated care by determining the difference between what the patient pays and what providing the care actually cost, the researchers report.

“The responses from the nonprofit hospitals make clear that the hospitals are all over the map in defining charity care,” Sen. Charles Grassley, R-Iowa, the most senior Republican on the Senate Finance Committee, says in a comment on the study. “We need common terms and measurements so taxpayers can have confidence that nonprofit hospitals are providing benefits commensurate with the billions of dollars in tax breaks they receive every year.”

A copy of the report is on the Web