CO-252: Attachment Required to Adjudicate Claim
The payer needs documentation to process your claim and nothing was submitted. Read the RARC codes to find out what is needed, gather the documents, and resubmit.
What Does CO-252 Mean?
CO-252 indicates the claim is pending because required documentation was not submitted. This is the provider's contractual obligation to supply — the patient has no financial responsibility while the claim is in this status. The denial is not a coverage dispute; the payer needs information to process the claim. The accompanying RARC codes are essential for determining exactly what documentation is required.
CARC 252 is the payer's request for additional documentation that was not submitted with the original claim. Unlike CARC 250 (wrong document received) or CARC 251 (incomplete document received), CARC 252 indicates that no attachment was provided at all. The payer cannot adjudicate the claim without the missing documentation.
This is one of the most common documentation-related denial codes. It is inherently vague — CO-252 by itself only tells you that something is missing. The critical information is in the accompanying RARC codes, which specify exactly what documentation the payer needs. There are 111 different RARC combinations that can accompany CO-252, ranging from missing clinical notes (N710) to missing Explanation of Benefits for coordination of benefits (N479) to missing medical reports (N714).
CARC 252 appears with Group Code CO, meaning the documentation deficiency is the provider's responsibility. The patient is not liable while the claim is pending due to missing documentation. The resolution is simple in concept — submit the required documentation — but execution requires carefully reading the RARC codes and providing exactly what the payer needs rather than sending generic medical records.
Common Causes
| Cause | Frequency |
|---|---|
| Required supporting documentation not submitted with claim The payer requires specific attachments to process the claim — such as clinical notes, test results, medical records, or operative reports — and none were submitted with the original claim | Most Common |
| Prior authorization documentation missing The claim requires documentation of prior authorization approval, but the authorization letter, reference number, or supporting clinical documentation was not included with the submission | Common |
| Medical necessity documentation not provided The payer requires documentation demonstrating medical necessity for the service, such as a letter of medical necessity, clinical evaluation, or diagnostic test results, and none was submitted | Common |
| Coordination of Benefits documentation missing The payer needs COB information or an Explanation of Benefits from the primary insurer to process the claim as secondary, and the required EOB was not attached | Common |
| Payer-specific attachment requirements not met Different payers have different documentation requirements — the provider did not meet the specific payer's attachment mandates for the type of service billed | Common |
How to Resolve
Identify the specific documentation needed by reading the RARC codes, gather the required materials, and resubmit the claim with the correct attachments.
- Decode the RARC requirements Identify which specific documentation is needed: N479 = Explanation of Benefits/COB, N710 = clinical notes, N712 = summary documentation, N714 = medical report, N716 = chart. Each RARC has a different resolution path.
- Verify the documentation exists Confirm the required documentation is available in the patient's medical record or can be obtained from the referring provider, primary insurer (for COB), or clinical department.
- Prepare and verify the documents Ensure the documents are complete, legible, properly dated, and match the specific claim. For COB requests, obtain the primary payer's EOB for the specific date of service.
- Resubmit with proper linking Submit the documentation linked to the claim reference number through the payer's preferred attachment method. Retain a copy and transmission confirmation for your records.
- Set follow-up reminders Do not assume resubmission resolves the issue. Set a follow-up date to verify the claim was reprocessed. If the claim is denied again, contact the payer to understand what is still missing.
CO-252 indicates the payer needs additional documentation to process the claim. This is a documentation request, not a coverage dispute. Submit the required attachments identified by the accompanying RARC codes and resubmit the claim rather than filing an appeal.
Common RARC Pairings
The RARC code tells you exactly what triggered the CO-252:
| RARC | Description |
|---|---|
| N479 | Missing Explanation of Benefits (Coordination of Benefits or Medicare Secondary Payer) Submit the primary payer's EOB and resubmit the claim → |
| N710 | Missing clinical notes Submit the clinical notes for the date of service → |
| N712 | Missing summary documentation Submit the required summary report → |
| N714 | Missing medical report Submit the specific medical report requested → |
| N716 | Missing chart documentation Submit the patient's chart for the date of service → |
How to Prevent CO-252
- Identify payer-specific attachment requirements for each service type before claim submission and include all required documentation upfront
- Build attachment requirement checklists into the billing workflow — flag services that commonly require clinical notes, prior auth documents, or COB information
- Verify that prior authorization documentation is complete and included with claims that require it
- Implement automated alerts when claims for services that typically require attachments are submitted without documentation
- Track CO-252 denial patterns by payer and service type to identify systematic documentation gaps
- Maintain current COB information and include primary payer EOBs when billing as secondary payer
General Prevention
- Build attachment requirement checklists into the billing workflow to ensure clinical notes, test results, and authorization documents are gathered before claims are generated
- Verify prior authorization documentation is complete and included with claims that require it
- Implement automated alerts in the billing system when claims for services that commonly require attachments are submitted without documentation
- Track CO-252 denial patterns by payer to identify systematic documentation gaps and proactively address them
- Maintain current Coordination of Benefits information and include primary payer EOBs when billing as secondary
Related Denial Codes
Sources
- https://etactics.com/blog/denial-code-co-252
- https://www.mdclarity.com/denial-code/252
- https://hcmsus.com/blog/co-252-denial-code
- Codes maintained by X12. Visit x12.org for official definitions.