MANCHESTER — The city is launching an independent audit of its primary ambulance service, American Medical Response, after the company acknowledged overbilling hundreds of patients since 2011.

The Board of Mayor and Aldermen voted last week to authorize independent auditor Kevin Buckley to review AMR’s billing practices.

AMR attributed the overbilling to human error. An in-house audit showed that 323 ambulance trips out of nearly 5,000 in 2011 and in the first months of 2012 had been “incorrectly billed.”

Expressing concerns that the billing problems could be more widespread, the aldermen voted last Tuesday for the audit.

Manchester Fire Chief James Burkush said AMR has cooperated so far in the effort to address the overbilling.

“They’ve been more than willing,” he said. “We believe all the bills have been adjusted and everyone has had refunds, but the city believes it’s in the best interest of everybody that they perform an independent audit and verify that.”

AMR forgave outstanding incorrect balances and issued $16,000 in refunds to patients who had already paid the incorrect bills.

The city’s rate for ambulance services is about $600, depending on how many miles the ambulance has to drive to get a patient to a hospital.

The audit is expected to be completed in two to three months.

Auditor Kevin Buckley could not be reached for comment.

tsiefer@unionleader.com