IOWA CITY, Iowa (AP) -

The University of Iowa Hospitals and Clinics is disputing a federal audit's finding that it should repay more than $550,000 for accidentally over-billing Medicare for a common cancer drug.

The Office of Inspector General of the U.S. Department of Health and Human Services released a report Tuesday concluding that billing errors caused UIHC to receive $826,000 more from Medicare in 2009 and 2010 than it was eligible.

The amount questioned is a tiny fraction of the $659 million that UIHC received from Medicare in those years for nearly 547,000 claims.

The hospital's response agrees that errors caused overbilling totaling about $271,000. But it is challenging a finding that seeks the repayment of $555,000 more, saying it accurately billed for Lupron injections based on the federal guidance available at the time.