CO 252 denial code

What CO-252 means

CO-252 means the payer received the claim but will not adjudicate it until it sees supporting documentation. Nothing has been judged non-covered or miscoded yet; the claim is parked pending an attachment. The rule for this code requires at least one remark code alongside it on the remittance, and that remark code identifies what the payer wants.

For Medicare, this pattern usually surfaces through the additional documentation request (ADR) process: the MAC selects a claim for review and asks for records before paying. Commercial payers use the same reason for operative reports on unlisted codes, invoices on high-cost items, and primary EOBs on secondary claims.

Because the group is CO, the amount is a contractual obligation while it stands; the patient cannot be billed for a claim your office has not yet documented to the payer’s satisfaction.

Common causes

• The billed code routinely requires an attachment (unlisted procedure codes need a descriptive report, some drugs and DME items need invoices), and none was sent.
• A secondary claim went out without the primary payer’s remittance information.
• The claim hit a prepayment review edit (dollar threshold, targeted service, provider under review) that always requests records.
• A Medicare ADR letter went unanswered because it landed at an unmonitored address or portal inbox.
• An attachment was sent but could not be matched to the claim: missing claim number, wrong patient identifiers, or a channel the payer does not link to claims.

How to fix and resubmit

1. Read the remark code paired with 252 and check the payer portal or your mail for a records request letter. Identify precisely what is wanted and the response deadline.
2. Gather the complete package: legible, signed notes covering the full date of service, plus whatever specific items the request names. Include the claim number and patient identifiers on every page.
3. Submit through the channel the payer specifies (for Medicare ADRs, the MAC’s portal is usually fastest) and keep proof of delivery. Meet the deadline; a missed one converts a fixable 252 into a harder denial.
4. Do not resubmit the claim itself unless the payer instructs you to. A duplicate claim will deny and muddy the record trail. The pending claim adjudicates once records arrive.
5. If the claim then denies on the merits, appeal that decision separately with any additional clinical support. If the documentation simply does not exist, write off the CO amount.

How to prevent it

Know your attachment-required codes and send documentation proactively with the claim where the payer supports it; check the payer’s policy for attachment methods. Always include the primary EOB data on secondary claims. Monitor payer portals for ADRs and records requests weekly, and keep correspondence addresses current with every payer. Track which services repeatedly draw documentation requests; a pattern can signal a prepayment review you should manage deliberately.

Related: CO-226 (requested information not provided) and CO-16 (claim lacks required information). Full series at the denial codes index.