Perhaps you're familiar with the following scenario: A hospital submits a short-stay inpatient (Part A) claim. An auditor, such as a RAC or MAC, reviews the claim and deems the admission to be not reasonable and necessary due to the hospital billing the wrong setting. The auditor issues a denial for the full amount of the claim. Although the hospital may rebill for certain Part B ancillary services before the timely filing limit, it may not bill for any of the other outpatient services denied as part of the inpatient claim.