Long-term care providers working with female physicians may be surprised to learn that Medicare pays them less than their male peers, according to a new analysis.

North Carolina researchers found female doctors were paid around $19,000 less annually than male physicians in 2012 based on an examination of more than 3 million Medicare reimbursement claims across 13 medical specialties.

The analysis originally found more than a $34,000 gap but then adjusted for productivity, years of experience and number of hours. The biggest gaps were in nephrology, rheumatology, pulmonary medicine and internal medicine.

“Perhaps most regrettably, we still do not have an answer as to why female providers are reimbursed less than their male counterparts,” the researchers wrote. Yet perhaps the data can “lead the medical profession (as a whole) towards a solution that can reverse this decades-old injustice.”

Findings appeared in Postgraduate Medical Journal online first on August 15.