CO 226 denial code

Claim adjustment reason code 226. Often reported as CO 226.

Provider did not send requested info

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 226 means

The payer asked the billing or rendering provider for information and it was never received, arrived late or was incomplete.

The claim stalled because the payer wanted something from you, such as medical records, an itemized bill or a form, and did not get what it needed in time.

This code always comes with at least one remark code that tells you what was missing. Read that first. The fix is usually to send the information and ask for reprocessing, rather than to rebill from scratch.

Group codes seen with 226

On a remittance, 226 comes after a group code. These are the ones it is most often reported with:

• CO 226 (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

• A records request letter went to an old address or was not routed to billing.
• Records were sent but did not include the pages or dates the payer asked for.
• The response went past the payer's deadline.
• An itemized bill, operative report or certification form was requested and not sent.
• The documents were sent without the claim number, so the payer could not match them.

What to do next

1. Read the remark codes to see exactly what the payer wanted.
2. Check your correspondence log for the original request and its due date.
3. Send the full set of requested documents with the claim number on each page.
4. Ask the payer whether to submit a reconsideration or just the records for reprocessing.
5. Fix the mail or portal routing that let the request go unanswered.

Related codes

• 227 (reason code) Patient did not send requested info
• 16 (reason code) Missing information or billing error
• 250 (reason code) Wrong attachment sent
• 252 (reason code) Attachment or documentation required