CO-252 denial code: an attachment or other documentation is required

Claim adjustment reason code 252 says: an attachment or other documentation is required to adjudicate this claim or service. The payer has not decided the claim. It has stopped until it gets something it asked for, or something its rules require for this service.

With group code CO, any amount left unpaid is the practice's responsibility, not the patient's. The claim is not lost, but it is not moving until the documentation arrives.

CARC 252 must always come with at least one remittance advice remark code (RARC). The remark code is the part that tells you what is missing.

The remark code on the same line of the payment file narrows "documentation" down to the actual document. Common ones:

Responding without reading the remark code is how practices send the wrong record and get the same denial back.

• The service always needs records. Unlisted procedure codes, modifier 22 for an unusually complex service, and some drugs and devices are reviewed with documentation before payment.
• A coverage policy requires documentation the claim doesn't show. Many Medicare coverage policies list what the record must contain, such as prior treatment or test results.
• The claim said an attachment was coming and it never arrived. An electronic claim can flag that paperwork is being sent separately (the PWK segment). If it doesn't reach the payer in time, the claim is denied.
• The payer selected the claim for review. Some payers request records on a sample of claims, or on a provider with an unusual billing pattern.

1. Find the remark code on the denied line and identify the exact document requested.
2. Pull the signed record for that date of service. It must be the note as written at the time, not a version edited afterwards.
3. Send it the way the payer accepts attachments: its portal, an electronic attachment, or the address and cover sheet it specifies. Medicare contractors publish their own routes.
4. Track it to a decision. Note the date sent and follow up if nothing comes back in the payer's stated timeframe.

• Know which codes always need records with each payer, and attach them with the first submission.
• Check the note against the coverage policy for the service: if the policy lists required documentation, make sure the note contains it before billing.
• Keep the original note separate from later additions, so what you send is defensible.
• When the claim says an attachment is coming, send it the same day.

CO-252 is a documentation problem, so it is prevented at the visit, not at billing.

Claira Health's AI agents flag a note that won't back the claim while it can still be fixed. The clinician always stays in charge of the record. Your team sees only what needs a decision, and approves every step. On a 20-minute call, we’ll walk through it using one of your own denials.

Want to know how many of your claims come back asking for records? Book a 20-minute call and bring one.