Avoid these common mistakes so you won't have to refund your MAC. If you're billing an incorrect number of drug units on your claims, you could be collecting thousands more than you deserve -- and you need to pay it back. That's the word from the OIG, whose latest report was released on April 22. The report, entitled "Review of Medicare Payments Exceeding Charges for Outpatient Services Processed by Noridian Administrative Services, LLC, in Jurisdiction 2 for the Period Jan. 1, 2006 through June 30, 2009," shed some light on common mistakes that Part B practices make, resulting in millions in repayments to Medicare. The method: To complete its audit, the OIG reviewed line items submitted to Noridian (a Part B MAC for four states) that had either a Medicare payment amount that exceeded the billed charge amount by at least $1,000; or three or more units of service. The OIG found 1,340 selected line items that fit these criteria over the audit period. The outcome: Only 359 of the 1,340 line items were paid correctly, the OIG found, meaning that the MAC paid 69 percent of these claims in error. By the time the OIG began researching the claims, providers had already refunded overpayments on 51 of the line items, leaving 930 remaining line items which amounted to overpayments totaling $6.2 million that remained inproviders' hands. Get to Know the Biggest Errors Among the 930 incorrect line items that the OIG reviewed were the following errors, the report indicates: When questioned, the Part B providers attributed the incorrect payments to clerical or billing system errors -- but that excuse won't help them keep the money. The OIG recommended that Noridian recover the remaining $6.2 million in overpayments and educate providers about appropriate coding and billing. What this means for you: MACs are going to be looking closely at the units of service that you report on your Part B claims and checking to ensure that you report the appropriate HCPCS codes. Tighten up your claims now to avoid MAC scrutiny by using the following tips: To read the complete OIG report, visit http://oig.hhs.gov/oas/reports/region9/91002019.pdf.