Your health insurance denied a claim: what to do

A denied claim doesn't automatically mean you owe the bill. Many denials are reversed once the right information is sent, and some denied amounts are the provider's responsibility, not yours.

Your Explanation of Benefits (EOB) lists a reason and sometimes a code. If you see one starting with two letters, they matter: CO means "contractual obligation", so the provider is generally responsible for that amount under its contract with your insurer. PR means "patient responsibility". Codes like CO-45 are routine price adjustments, not denials.

• Missing prior authorization or referral: usually the provider's paperwork. They can ask for a retroactive authorization or appeal.
• Other insurance (coordination of benefits): your insurer needs to know whether you have other coverage. Answering their question often gets it reprocessed.
• Filed too late (timely filing): in-network providers generally have to absorb this, not pass it to you, if you gave them your insurance information in time.
• Not medically necessary: a letter from your doctor explaining why you needed the care makes an appeal much stronger.
• Missing or incorrect information: the provider can correct the code and resubmit.

For most job-based and marketplace plans, you can file an internal appeal within 180 days of the denial notice. If the insurer upholds the denial, you can usually ask for an external review by an independent reviewer, generally within 4 months of the final denial. Ask the provider to put the account on hold while the appeal is open.

Deadlines and rules vary by plan, and Medicare and Medicaid have their own appeal processes. This guide is educational, not legal advice.