CO-163: Attachment/Documentation Not Received
Required documentation was not received. Resubmit the claim with all referenced attachments properly linked to the claim.
What Does CO-163 Mean?
CO-163 is the standard pairing for this denial. The payer is treating the missing documentation as a contractual issue — the claim cannot be processed without the referenced attachments, and the provider is responsible for supplying them. Under CO, you cannot bill the patient for this denial. The resolution is to locate and submit the missing documentation, then have the claim reprocessed.
When CARC 163 appears on a remittance, the payer is telling you that the claim referenced supporting documentation — such as medical records, operative notes, test results, or pre-authorization letters — but that documentation never arrived. The payer cannot adjudicate the claim without the referenced materials, so it is denied pending receipt of the missing attachments.
This is one of the more frustrating denials because the clinical service was likely appropriate and properly coded. The issue is purely logistical: either the documentation was never sent, it was sent but failed to transmit (common with fax and electronic attachment systems), or it was sent but could not be matched to the claim because of a reference number mismatch. In some cases, the payer received the documents but classified them as incomplete or illegible, which has the same effect as not receiving them.
CARC 163 is almost always paired with Group Code CO, making it a contractual adjustment that the provider must resolve. The fix is straightforward: gather the required documentation, verify it meets the payer's format and submission requirements, and resubmit. The critical detail is ensuring the attachment control number or claim reference links the documents to the correct claim. Without that link, the payer's system may receive the documents but fail to associate them with the pending claim, resulting in a repeat denial.
Common Causes
| Cause | Frequency |
|---|---|
| Required attachments not submitted with the claim The claim referenced supporting documentation (medical records, operative notes, test results, pathology reports) that was never sent to the payer, either because the provider forgot to include them or the submission process did not bundle them with the claim | Most Common |
| Electronic transmission failure The documentation was sent electronically but failed to transmit properly due to system errors, incorrect attachment format, file size limitations, or connectivity issues between the provider's system and the payer's portal | Most Common |
| Fax or mail delivery failure Physical documentation sent via fax or mail did not reach the payer due to incorrect fax numbers, failed transmissions, lost mail, or documents being routed to the wrong department | Common |
| Documentation mismatch with claim reference The documentation was sent but the claim reference number, patient identifiers, or attachment control number did not match, preventing the payer from associating the documents with the correct claim | Common |
| Incomplete or illegible documentation The documentation was received but was incomplete, illegible, or lacked required elements such as signatures, dates, or specific clinical details, causing the payer to treat it as not received | Occasional |
| Payer-specific submission requirements not followed The documentation was submitted but did not conform to the payer's specific format, portal, or submission method requirements (e.g., sent via fax when the payer requires electronic attachment submission) | Occasional |
How to Resolve
Identify the missing documentation, verify submission requirements, and resubmit the claim with all referenced attachments properly linked.
- Identify which attachments are missing Review the original claim and ERA to determine the specific documentation the payer expected but did not receive.
- Verify your transmission records Check fax confirmations, electronic submission logs, or mail tracking to determine if the documentation was previously sent.
- Resubmit with all documentation Gather the required documents, ensure they meet payer format requirements, and resubmit the claim with the documentation properly linked via attachment control number.
- Confirm receipt and track to adjudication Follow up with the payer to confirm the documentation was received and matched to the claim. Track the claim through reprocessing to resolution.
This is a standard contractual adjustment. The amount is a provider write-off per your payer contract and cannot be billed to the patient.
Common RARC Pairings
The RARC code tells you exactly what triggered the CO-163:
| RARC | Description |
|---|---|
| MA04 | Secondary payment cannot be considered without the identity of or payment information from the primary payer. The information was either not reported or was illegible. |
| N479 | Alert: Refer to your provider manual or payer website for additional claim submission requirements. |
| N381 | Alert: Consult your contractual agreement for restrictions, billing, and payment information related to these charges. |
How to Prevent CO-163
- Use a pre-submission checklist to verify all referenced attachments are included before sending claims
- Implement electronic attachment submission with delivery confirmation for a traceable record
- Maintain a document tracking system that logs every attachment with dates, methods, and confirmation numbers
- Verify payer-specific documentation requirements and submission methods before claim submission
- Set up automated alerts for claims that reference attachments to ensure documents are bundled
General Prevention
- Implement a pre-submission checklist that verifies all referenced attachments are included before the claim is sent to the payer
- Use electronic attachment submission methods with delivery confirmation to create a traceable record of all documentation sent
- Maintain a document tracking system that logs every attachment sent with each claim, including dates, methods, and confirmation numbers
- Verify payer-specific documentation requirements and submission methods before sending claims that require attachments
- Set up automated alerts for claims that reference attachments to ensure the documents are bundled with the claim submission
- Retain copies of all submitted documentation and transmission confirmations for at least the payer's timely filing period
Also Filed As
The same CARC 163 may appear with different Group Codes:
Related Denial Codes
Sources
- https://www.mdclarity.com/denial-code/163
- https://portal.ct.gov/-/media/ohs/health-it-advisory-council/apcd-advisory-group/data-submission-guide-workgroup/meeting-materials/6-30-22/carc-codes_final.pdf
- https://ambci.org/medical-billing-and-coding-certification-blog/guide-to-claim-adjustment-reason-codes-carcs
- Codes maintained by X12. Visit x12.org for official definitions.