Which denial codes will I meet most?

A handful of codes cover most of what lands on your desk. Learn these and the rest can be looked up.

• CO-16, missing information. The claim lacks something the payer needs. The paired remark code names the exact field. Usually the friendliest kind: add what is missing and resend.
• CO-197, no prior authorization. The service needed the payer’s approval before it happened. Sometimes a backdated authorization is possible, which is why it is worth asking rather than writing off.
• CO-18, duplicate claim. The payer already has this one. Check whether the original paid before doing anything else.
• CO-29, filed too late. The filing deadline passed. Proof that the original went out inside the window is the whole appeal.
• CO-45, over the allowed amount. Not really a denial at all. It is the ordinary contractual write-off, provided the allowed amount matches your contract. If it is below your contracted rate, that is an underpayment to chase, not a write-off.
• CO-97, bundled. Payment for this service is included in another service already paid.
• CO-50, not medically necessary. The payer’s policy did not accept the diagnosis as supporting the service.
• CO-27, coverage terminated. The patient was not active on the date of service. See What if the coverage was not active that day?.
• PR-1, PR-2, PR-3. Deductible, coinsurance and copay. These are not denials at all: the money simply belongs to the patient.

You never have to memorize them. Ask what a code means on the claim in front of you and it is read back in plain English.