CO-252 Denial Code: Additional Documentation Required

The CO-252 denial code means an attachment or other documentation is required before the payer can adjudicate the claim — it needs to see records, not a corrected claim. A remark code on the remittance names the exact document the payer wants. Treat CO-252 as a records request with a deadline: send precisely what is asked and the claim resumes processing.

What is the CO-252 denial code? CO-252 is a Claim Adjustment Reason Code (CARC) indicating an attachment or other documentation is required to adjudicate the claim; it must be paired with a remark code specifying the documentation the payer needs.

Undeny's Take

CO-252 is the friendliest "denial" you will get, and the one practices fumble most by overreacting. The payer is not saying no — it is saying "show me." The mistake is dumping the entire chart or, worse, ignoring it until it ages out. Read the remark code, send precisely what it asks for (often a single session note, a treatment plan, or a testing report), and meet the response deadline. In behavioral health, a tight, relevant note beats a hundred-page record every time; payers reviewing a targeted submission turn it around faster and deny less.

CO-252 as a Records Request

CO-252 corresponds to X12 code 252: "An attachment/other documentation is required to adjudicate this claim/service," with the rule that at least one remark code (a Remittance Advice Remark Code that is not an ALERT, or an NCPDP reject code) must accompany it. The CO group code makes the held amount a contractual obligation while the documentation is outstanding, so it is not patient responsibility. The remark code is what tells you which record to provide.

What Prompts a Documentation Request

The payer's policy requires supporting documentation for the service or diagnosis.
A targeted medical-necessity or utilization review was triggered for the claim.
The service type (such as psychological testing or a higher level of care) routinely requires records.
Documentation was expected with the original claim and was not attached.

Responding to a CO-252

Read the remark code on the remittance — it names the specific documentation the payer requires.
Gather exactly what is requested (for example, the session note, treatment plan, or testing report), not the entire chart.
Submit the documentation through the payer's required channel and within its response window.
If the payer denies after you supplied complete records, appeal with proof of the submission, or draft it with the appeal generator.

CO-252 and Related Information Codes

CO-252 is a documentation request, related to other information codes. CO-16 means the claim lacks information or has a submission error. CO-96 means non-covered charges, sometimes resolved by the same records a CO-252 requests. Browse the full set under denial codes.

Frequently Asked Questions

What does CO-252 mean?

CO-252 means additional documentation is required to adjudicate the claim. The payer is holding the claim until it receives records, and a remark code on the remittance names exactly what to send.

Can I bill the patient for a CO-252 denial?

No. CO-252 carries the Contractual Obligation group code, so the amount is not patient responsibility while documentation is outstanding. Provide the requested records to move the claim forward.

What documentation does a CO-252 require?

Whatever the accompanying remark code specifies — commonly a session note, treatment plan, or testing report. Send the targeted record requested rather than the entire chart, and meet the payer's response deadline.

Is CO-252 a denial or a request?

It is effectively a request for information. The claim is not finally denied; it is pending the documentation. Respond promptly and completely and the payer resumes adjudication.

Informational only — not legal, medical, or billing advice. Always verify against your current payer contract and policy.

Fix CO-252 denials automatically

Undeny identifies the records the remark code requests and drafts your response in seconds. Generate an appeal · Browse denial codes