OIG Report (Audit): Potential Vulnerabilities in CMS’s Oversight of Medicare Providers’ Billing of Selected Outpatient Drugs

The OIG issued this data brief (Report No. OAS-25-09-090) on October 23, 2026, based on an analysis of Medicare Part B claims data with dates of service from April 1, 2024, through March 31, 2025. The analysis examined claim lines where providers billed outpatient drugs using procedure codes that did not match the procedure codes associated with the drug codes in CMS crosswalk files. CMS crosswalk files are the reference documents providers use to select the correct procedure code when billing for a specific administered drug. OIG identified 160,918 Part B claim lines involving 577 unique mismatched procedure codes. Six procedure codes accounted for 62 percent of those claim lines. Critical access hospitals and short-term acute-care hospitals together billed 99 percent of the mismatched claim lines, with a single short-term acute-care hospital responsible for 7 percent of the total. OIG identified two specific oversight vulnerabilities. First, neither CMS nor its Medicare Administrative Contractors had system edits in place to detect or reject claims where the procedure code billed did not correspond to the drug code on the same claim line. Second, provider education activities conducted by CMS and the MACs did not address the requirement to use procedure codes that match those in the CMS crosswalk files when billing outpatient drugs. The data brief contains no formal recommendations to CMS. OIG states that the findings are intended to help CMS and the MACs strengthen future oversight of outpatient drug billing and protect Medicare program funds.