SACRAMENTO (AP) — California paid at least $4 billion over four years in questionable Medi-Cal premiums and claims because it failed to follow up on eligibility discrepancies, according to an audit released Tuesday.

From 2014 through 2017, more than 450,000 people marked as eligible for Medi-Cal in the state’s system were listed as ineligible in county systems, the California auditor’s office said. Half of those discrepancies persisted for more than two years.

“Some eligible individuals may have encountered unnecessary hardship and been inappropriately denied services,” said a summary that accompanied the report.

The Department of Health Care Services, which administers California’s Medicaid program, said in a statement that it agrees with the auditor’s recommendations, and it is taking appropriate corrective actions.

At least 170,000 people were listed as able to receive benefits after their temporary eligibility statuses had expired, “which may amass significant costs to the state,” the summary said. Some residents received temporary benefits for more than three years after their eligibility ran out, the report found.

Auditors recommended the department recover erroneous payments when possible and “implement protocols to ensure timely resolution of discrepancies.”

The department was also urged to assist counties in addressing the problems.

The department said in a statement that it is “implementing a quality control process that will identify system discrepancies, and will work to ensure that counties have the resources and technology needed to appropriately resolve discrepancies.” It will report back to the auditor’s office on its progress by June 2019, the department said.

More than 13 million Californians are enrolled in Medi-Cal, which provides low-income residents with services including general health care, emergency services, dental work and mental health and substance abuse treatments.