CO 285 denial code

Claim adjustment reason code 285. Often reported as CO 285.

Appeal procedures not followed

Unofficial reference. This is our own plain-English explanation, not the official code text. Payer rules differ. Verify with the payer and the official X12 code list. AlphaPrefix is not affiliated with X12, CMS or any payer. Data last updated Nov 11, 2026.

What 285 means

The payer did not consider the appeal because it was not filed according to the payer's appeal process.

This code concerns the appeal, not the original claim. The appeal may have gone to the wrong place, used the wrong form, skipped a required level, or lacked something the process requires.

The original denial still stands. Read the payer's appeal instructions carefully and file again the right way if time allows.

Group codes seen with 285

On a remittance, 285 comes after a group code. These are the ones it is most often reported with:

• CO 285 (Contractual Obligation): The provider's side of the ledger. The reduction comes from the payer contract or a rule the provider has to follow, and the patient normally cannot be billed for it.

The payer chooses the group code for each adjustment, so the same reason code can appear with another group code on your remittance. Read the two together. More about group codes.

Common causes

• The appeal was sent to the wrong address, fax, or portal.
• A required form, signature, or level of review was skipped.
• A corrected claim was sent when the payer required a formal appeal, or the reverse.

What to do next

1. Read the payer's appeal process for the claim type and level of appeal.
2. Resend the appeal through the right channel with the required form and documents.
3. Check how much appeal time remains before you resubmit.

Related codes

• 286 (reason code) Appeal filed too late
• 29 (reason code) Timely filing limit has passed