CO 226 denial code

What CO-226 means

CO-226 means the payer asked the billing or rendering provider for information it needed to process the claim, and the answer never arrived, arrived late, or arrived incomplete. The claim then denied by default. The remittance must carry at least one remark code alongside 226, and that remark code tells you what the payer wanted: read it before doing anything else.

The CO group code makes the denied amount a contractual obligation. The patient cannot be billed because the provider side failed to respond; the fix is to respond now and get the claim reprocessed.

Common causes

• A development letter or additional documentation request (ADR) went to an old address or an unmonitored fax line, so nobody answered it.
• The request was received but missed its deadline while the records were being gathered.
• The response was incomplete (pages missing, an unsigned note, a date range that did not cover the service).
• Requested credential, license, or supervision details for the rendering provider were never supplied.
• The response went to the wrong place: a general claims address instead of the review unit named in the letter.

How to fix and resubmit

1. Read the remark code paired with 226 on the remittance, then locate the payer’s original request in your mail log, fax archive, and payer portal. Confirm exactly what was asked and when it was due.
2. Assemble the complete package: every document named in the request, covering the full date span, signed and legible. Half-answers produce a second 226.
3. Submit it through the channel the payer specifies. For Medicare, that is typically a redetermination through the MAC (portal submission is fastest), filed within 120 days of the remittance date. For commercial payers, check the payer’s policy; some reopen the claim on receipt of records, others require a formal appeal.
4. Do not submit a brand-new claim. A duplicate will deny and can complicate the appeal trail. The original claim needs to be reopened or appealed with the records attached.
5. If the records requested do not exist or cannot support the service, write off the CO amount and treat it as a documentation-process failure to fix upstream.

How to prevent it

Audit the contact details every payer has on file (pay-to address, correspondence address, fax) and update them whenever the office moves or restructures; use an NPI lookup to check what is publicly on record. Route all payer correspondence to one logged inbox with an owner and a deadline tracker. Check payer portals for open development requests weekly; some payers post there without mailing anything. When a request arrives, calendar the due date the same day and aim to respond a week early.

Related: CO-252 (attachment required to adjudicate) and CO-16 (claim lacks required information). Browse the denial codes index for more.