I have a question about how far back a payer can audit charges. I think Medicare can go back 3 years. For commercial payers, example Highmark Pennsylvania, is there a time frame? Can they follow Medicare of 3 years? Is it based on your contract? Can they audit a code if they just implemented a policy May 2017 and look back to 2014 on this code? What if the payer policy contradicts what is being audited, payer doesn't specify units billed but is denying for units billed. Is there anything a practice can do to challenge these audits when policy doesn't back up the audit and policy just implemented? Please help!