OIG lists the following items as specific regulatory risks most frequently subject to investigation and audit:

1. Billing for items or services not rendered
2. Submitting claims for supplies and services that are not reasonable and necessary
3. Double billing
4. Billing for non-covered services
5. Failure to properly use coding modifiers
6. "Clustering" (using only a few codes on the theory that it will average out)
7. "Upcoding" (using a higher reimbursement code than the code reflecting the service rendered)
8. Inappropriate balance billing
9. Routine waiver of co-payments and billing third-party insurance only
10. Discounts and professional courtesy
11. Improper billing for incident-to services
12. Improper reassignment of physician billing numbers
13. Failure to refund credit balances due to patients and payers
14. Billing for services provided by unqualified or unlicensed clinical personnel