Medicare paid $30 million for ambulance rides for which no record exists that patients got medical care at their destination, the place where they were picked up or other critical information.
The mystery ambulance rides are part of a bigger problem with Medicare payments for transporting patients, according to a federal audit being released Tuesday.
The Department of Health and Human Services' inspector general's office also found that some urban ambulance services got paid for an average distance of more than 100 miles per ride. That contrasts with a national average of just 10 miles for urban ambulance rides.
Four major metro areas seemed to be breeding grounds for ambulance schemes. Philadelphia, Los Angeles, New York and Houston accounted for about half of the questionable rides and payments. Medicare has barred new ambulance companies from joining the program in Houston and Philadelphia, and the report recommends a similar approach in certain other places.
Across the country, 1 in 5 ambulance companies had at least some questionable billings.
"Medicare payments for ambulance transports have increased in recent years, and investigators have uncovered a variety of fraud schemes involving ambulance suppliers," the report said.
The audit involves medical claims dating to the first six months of 2012, but the inspector general's office said it believes the findings reflect continuing weaknesses in Medicare's efforts against fraud. A Medicare spokesman says the agency has taken action since the auditors privately shared their findings last year.