CO-252 — Missing Documentation / Attachment Required

Denial Identifier

• Primary CARC: CO-252 — "An attachment/other documentation is required to adjudicate this claim/service. At least one Remark Code must be provided..." (X12)
• Related CARCs: 226 (info requested from billing/rendering provider not provided or insufficient/incomplete), 227 (info requested from patient/insured/responsible party not provided or insufficient/incomplete), 250 (attachment received was the incorrect document — the expected attachment is still missing), 251 (attachment received was incomplete or deficient), 163/164 (attachment referenced but not received / not received timely)
• Common RARC: N686 — "Missing/incomplete/Invalid questionnaire needed to complete payment determination." Specific missing-document RARCs vary widely by document type (e.g., operative note, medical record, invoice).

Plain-Language Meaning

• The payer cannot finish processing this claim without additional supporting documentation (medical records, operative note, invoice, questionnaire, etc.) that either was never sent, was the wrong document, or was incomplete.

Why the Claim Was Denied

• Clinical documentation: required record (operative note, medical necessity documentation, itemized invoice) not attached to the original submission
• Claim construction: attachment control number referenced on the claim but the actual document was not transmitted
• Patient/COB information: a required patient questionnaire (e.g., accident/COB questionnaire) was not completed

Information the Biller Must Review

• The specific RARC identifying the exact document needed, original claim's attachment reference (if any), the actual medical record/documentation available, payer portal for document-submission requirements and deadlines.

What Needs to Be Corrected

• Claim correction: Not a data-field fix — the missing item is a document, not a claim field.
• Upstream correction: Submit the correct, complete documentation through the payer's required channel (portal, fax, EDI attachment) within the payer's response deadline.

Resolution Workflow

• Identify the exact document requested from the RARC/payer correspondence.
• Confirm the document exists in the medical record/HIM system.
• Submit the complete, correct document through the payer's specified channel before the response deadline.
• If the document does not exist or is incomplete, route to the clinical department/HIM for completion.
• Document submission date and method.
• Escalate if the payer's deadline is shorter than the time needed to obtain the document from the clinical department.

Department Most Likely Responsible

• Resolves current claim: HIM, Denials/Follow-Up. Prevents recurrence: Clinical Department/HIM — ensure documentation is complete and attached at time of original claim submission for document-heavy service types.

Prevention Control

• Pre-submission checklist requiring attachments for known documentation-heavy service types (e.g., DME, certain surgical claims); electronic attachment (275 transaction) workflows to reduce lost/incomplete paper submissions.

Escalation Trigger

• Requested documentation does not exist in the record (potential compliance/documentation- improvement issue); payer response deadline cannot realistically be met.

Sample Scenario

• Scenario: DME claim denied CO-252/N686.
• Finding: Required physician order/questionnaire was completed but not attached to the original electronic claim.
• Action: Complete order and questionnaire submitted through the payer's attachment portal before the response deadline.

Resolution path at a glance

AI Search Terms / Synonyms

• CO252; CO-252; attachment required; missing documentation denial; medical records requested; N686.

AI Answer Guardrail

• Confirm exactly which document the RARC is requesting and the payer's submission deadline before advising on documentation submission or appeal.

Sources

• X12 CARC list; X12 RARC list