Official X12 description
“An attachment/other documentation is required to adjudicate this claim/service.”
Source: X12 Claim Adjustment Reason Codes. The X12 External Code Lists are the single authoritative source for every CARC descriptor — always verify against the current release before building a claim-scrub rule.
What CARC 252 actually means
CARC 252 is a 'missing attachment' denial: the payer's edits require supporting documentation (op note, invoice, pathology report, ABN, etc.) before it will adjudicate this claim, and that documentation did not reach the payer. The cure is almost always a corrected claim with the required attachment — a paper-based PWK segment, a clearinghouse-delivered PDF, or fax with cover sheet, depending on payer preference.
Common root causes
- Claim was submitted without a required attachment (op note for unlisted codes, pathology for surgery, invoice for NOC drugs, ABN for non-covered service).
- PWK (paperwork) segment on the 837 did not reach the payer or did not match a fax/upload that was sent separately.
- Attachment type or format did not meet the payer's companion guide.
Prevention checklist
- Build payer-specific attachment rules into the scrubber — block submission when the billed code has a known documentation trigger.
- Standardize the PWK workflow: one record-locator number per claim, matched fax cover sheet sent within 24 hours of claim submission.
Appeal strategy — step by step
Most CARC 252 denials clear faster with the right remediation than with a formal appeal. Work the steps in order and escalate only when a lower-effort path has been ruled out.
- 1Rebill as a corrected claim (frequency 7) with the attachment properly flagged in the PWK segment; a formal appeal is rarely needed.
- 2Include the clearinghouse tracking ID and the original submission date to preserve timely-filing posture.
Sample appeal-letter language for CARC 252
Edit the bracketed fields before sending. This template is a starting point; a payer-specific appeal form may still be required — check the provider portal first.
Payer-specific notes
Payer-specific behavior for CARC 252 publishes here as the QuickIntell anonymized denial ETL ingests sufficient volume. In the meantime, consult the payer directory for the relevant provider manual and appeal form.
How common is CARC 252?
Out of 306 seeded CARCs, ranked by combined US monthly search volume for "CARC 252", "CO-252 denial", and "denial code 252".
Platform frequency ranks publish once the anonymized denial-rate pipeline reaches the publication threshold (strategy §12 Phase 2).
How QuickRCM prevents CARC 252
QuickRCM catches the root causes above before the 837 leaves the clearinghouse:
- Claim-scrub rules fire on every root cause listed above — the scrub references the same X12 CAS segment logic that drives the denial, so what the payer checks, QuickRCM checks first.
- When a denial lands, QuickRCM routes it to the correct worker with the documentation bundle already attached (op note, LCD citation, modifier rationale, EOB, primary 835).
- Appeal templates tuned to each CARC (including this one) pull the supporting facts from the claim and fill the bracketed fields automatically.
CAQH CORE code combinations for CARC 252
Under the CAQH CORE Payment and Remittance Uniform Use rule, health plans may pair CARC 252 only with the remark codes and group codes below for the defined business scenario 1 (Additional information required: missing, invalid or incomplete documentation). A combination outside this list on an 835 is itself a payer compliance issue worth raising.
| RARC | Remark description | Group code | Scenario |
|---|---|---|---|
| M19 | Missing oxygen certification/re-certification. | CO or PI | 1 |
| M21 | Missing/incomplete/invalid place of residence for this service/item provided in a home. | CO or PI | 1 |
| M23 | Missing invoice. | CO or PI | 1 |
| M29 | Missing operative note/report. | CO or PI | 1 |
| M30 | Missing pathology report. | CO or PI | 1 |
| M31 | Missing radiology report. | CO or PI | 1 |
| M42 | The medical necessity form must be personally signed by the attending physician. | CO or PI | 1 |
| M60 | Missing Certificate of Medical Necessity. | CO or PI | 1 |
| M125 | Missing/incomplete/invalid information on the period of time for which the service/supply/equipment will be needed. | CO or PI | 1 |
| M127 | Missing patient medical record for this service. | CO or PI | 1 |
| M130 | Missing invoice or statement certifying the actual cost of the lens, less discounts, and/or the type of intraocular lens used. | CO or PI | 1 |
| M131 | Missing physician financial relationship form. | CO or PI | 1 |
| M132 | Missing pacemaker registration form. | CO or PI | 1 |
| M135 | Missing/incomplete/invalid plan of treatment. | CO or PI | 1 |
| M141 | Missing physician certified plan of care. | CO or PI | 1 |
| M142 | Missing American Diabetes Association Certificate of Recognition. | CO or PI | 1 |
| M143 | The provider must update license information with the payer. | CO or PI | 1 |
| 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. | CO or PI | 1 |
| MA27 | Missing/incomplete/invalid entitlement number or name shown on the claim. | CO or PI | 1 |
| MA64 | Our records indicate that we should be the third payer for this claim. We cannot process this claim until we have received payment information from the primary and secondary payers. | CO or PI | 1 |
| MA75 | Missing/incomplete/invalid patient or authorized representative signature. | CO or PI | 1 |
| MA76 | Missing/incomplete/invalid provider identifier for home health agency or hospice when physician is performing care plan oversight services. | CO or PI | 1 |
| MA81 | Missing/incomplete/invalid provider/supplier signature. | CO or PI | 1 |
| MA88 | Missing/incomplete/invalid insured's address and/or telephone number for the primary payer. | CO or PI | 1 |
| MA92 | Missing plan information for other insurance. | CO or PI | 1 |
| MA111 | Missing/incomplete/invalid purchase price of the test(s) and/or the performing laboratory's name and address. | CO or PI | 1 |
| N3 | Missing consent form. | CO or PI | 1 |
| N4 | Missing/incomplete/invalid prior insurance carrier(s) EOB. | CO or PI | 1 |
| N26 | Missing itemized bill/statement | CO or PI | 1 |
| N28 | Consent form requirements not fulfilled. | CO or PI | 1 |
| N40 | Missing radiology film(s)/image(s). | CO or PI | 1 |
| N42 | Missing mental health assessment. | CO or PI | 1 |
| N50 | Missing/incomplete/invalid discharge information. | CO or PI | 1 |
| N80 | Missing/incomplete/invalid prenatal screening information. | CO or PI | 1 |
| N146 | Missing screening document. | CO or PI | 1 |
| N170 | A new/revised/renewed certificate of medical necessity is needed. | CO or PI | 1 |
| N175 | Missing review organization approval. | CO or PI | 1 |
| N178 | Missing pre-operative images/visual field results. | CO or PI | 1 |
| N186 | Non-Availability Statement (NAS) required for this service. Contact the nearest Military Treatment Facility (MTF) for assistance. | CO or PI | 1 |
| N191 | The provider must update insurance information directly with payer. | CO or PI | 1 |
| N204 | Services under review for possible pre-existing condition. Send medical records for prior 12 months. | CO or PI | 1 |
| N214 | Missing/incomplete/invalid history of the related initial surgical procedure(s). | CO or PI | 1 |
| N221 | Missing Admitting History and Physical report. | CO or PI | 1 |
| N223 | Missing documentation of benefit to the patient during initial treatment period. | CO or PI | 1 |
| N241 | Incomplete/invalid review organization approval. | CO or PI | 1 |
| N331 | Missing/incomplete/invalid physician order date. | CO or PI | 1 |
| N350 | Missing/incomplete/invalid description of service for a Not Otherwise Classified (NOC) code or for an Unlisted/By Report procedure. | CO or PI | 1 |
| N375 | Missing/incomplete/invalid questionnaire/information required to determine dependent eligibility. | CO or PI | 1 |
| N391 | Missing emergency department records. | CO or PI | 1 |
| N393 | Missing progress notes/report. | CO or PI | 1 |
| N395 | Missing laboratory report. | CO or PI | 1 |
| N398 | Missing elective consent form. | CO or PI | 1 |
| N401 | Missing periodontal charting. | CO or PI | 1 |
| N403 | Missing facility certification. | CO or PI | 1 |
| N439 | Missing anesthesia physical status report/indicators. | CO or PI | 1 |
| N445 | Missing document for actual cost or paid amount. | CO or PI | 1 |
| N451 | Missing Admission Summary Report. | CO or PI | 1 |
| N453 | Missing Consultation Report. | CO or PI | 1 |
| N455 | Missing Physician Order. | CO or PI | 1 |
| N457 | Missing Diagnostic Report. | CO or PI | 1 |
| N459 | Missing Discharge Summary. | CO or PI | 1 |
| N461 | Missing Nursing Notes. | CO or PI | 1 |
| N465 | Missing Physical Therapy Notes/Report. | CO or PI | 1 |
| N467 | Missing Tests and Analysis Report. | CO or PI | 1 |
| N473 | Missing certification. | CO or PI | 1 |
| N475 | Missing completed referral form. | CO or PI | 1 |
| N477 | Missing Dental Models. | CO or PI | 1 |
| N479 | Missing Explanation of Benefits (Coordination of Benefits or Medicare Secondary Payer). | CO or PI | 1 |
| N481 | Missing Models. | CO or PI | 1 |
| N485 | Missing Physical Therapy Certification. | CO or PI | 1 |
| N487 | Missing Prosthetics or Orthotics Certification. | CO or PI | 1 |
| N489 | Missing referral form. | CO or PI | 1 |
| N491 | Missing/Incomplete/Invalid Exclusionary Rider Condition. | CO or PI | 1 |
| N493 | Missing Doctor First Report of Injury. | CO or PI | 1 |
| N495 | Missing Supplemental Medical Report. | CO or PI | 1 |
| N497 | Missing Medical Permanent Impairment or Disability Report. | CO or PI | 1 |
| N499 | Missing Medical Legal Report. | CO or PI | 1 |
| N501 | Missing Vocational Report. | CO or PI | 1 |
| N503 | Missing Work Status Report. | CO or PI | 1 |
| N542 | Missing income verification. | CO or PI | 1 |
| N555 | Missing medication list. | CO or PI | 1 |
| N590 | Missing independent medical exam detailing the cause of injuries sustained and medical necessity of services rendered. | CO or PI | 1 |
| N594 | Records reflect the injured party did not complete an Application for Benefits for this loss. | CO or PI | 1 |
| N595 | Records reflect the injured party did not complete an Assignment of Benefits for this loss. | CO or PI | 1 |
| N596 | Records reflect the injured party did not complete a Medical Authorization for this loss. | CO or PI | 1 |
| N667 | Missing prescription. | CO or PI | 1 |
| N668 | Incomplete/invalid prescription. | CO or PI | 1 |
| N678 | Missing post-operative images/visual field results. | CO or PI | 1 |
| N680 | Missing/Incomplete/Invalid date of previous dental extractions. | CO or PI | 1 |
| N681 | Missing/Incomplete/Invalid full arch series. | CO or PI | 1 |
| N682 | Missing/Incomplete/Invalid history of prior periodontal therapy/maintenance. | CO or PI | 1 |
| N683 | Missing/Incomplete/Invalid prior treatment documentation. | CO or PI | 1 |
| N685 | Missing/incomplete/Invalid questionnaire needed to complete payment determination. | CO or PI | 1 |
| N686 | Missing/incomplete/Invalid questionnaire needed to complete payment determination. | CO or PI | 1 |
| N706 | Missing documentation. | CO or PI | 1 |
| N707 | Incomplete/invalid orders. | CO or PI | 1 |
| N708 | Missing orders. | CO or PI | 1 |
| N710 | Missing notes. | CO or PI | 1 |
| N712 | Missing summary. | CO or PI | 1 |
| N714 | Missing report. | CO or PI | 1 |
| N716 | Missing chart. | CO or PI | 1 |
| N718 | Missing documentation of face-to-face examination. | CO or PI | 1 |
| N729 | Missing patient medical/dental record for this service. | CO or PI | 1 |
| N737 | Missing Sleep Study Report. | CO or PI | 1 |
| N739 | Missing Vein Study Report. | CO or PI | 1 |
| N745 | Missing Ambulance Report. | CO or PI | 1 |
| N749 | Missing Blood Gas Report. | CO or PI | 1 |
| N764 | Missing/incomplete/invalid Hematocrit (HCT) value. | CO or PI | 1 |
| N785 | Missing current radiology film/images. | CO or PI | 1 |
| N791 | Missing history & physical report. | CO or PI | 1 |
| N796 | Missing/incomplete/invalid Hemoglobin (Hb or Hgb) value. | CO or PI | 1 |
| N836 | Provider W9 or Payee Registration not on file. | CO or PI | 1 |
| N890 | Electronic Visit Verification Data Element Requirements were not met. | CO or PI | 1 |
| N893 | Missing/incomplete/invalid child medical evaluation form/checklist. | CO or PI | 1 |
| N896 | Missing/incomplete/invalid trauma activation sheet. | CO or PI | 1 |
| N897 | Missing/incomplete/invalid proof of member payment. | CO or PI | 1 |
| N899 | Missing Initial Evaluation Report. | CO or PI | 1 |
| N900 | Missing Therapy Notes/Report. | CO or PI | 1 |
| N902 | Missing Health Risk Assessment (HRA). | CO or PI | 1 |
Frequently asked questions — CARC 252
What does CARC 252 mean?
CARC 252 is an X12 Claim Adjustment Reason Code. The official definition is: "An attachment/other documentation is required to adjudicate this claim/service." In plain English, the payer is telling you cARC 252 is a 'missing attachment' denial: the payer's edits require supporting documentation (op note, invoice, pathology report, ABN, etc.) before it will adjudicate this claim, and that documentation did not reach the payer. The cure is almost always a corrected claim with the required attachment — a paper-based PWK segment, a clearinghouse-delivered PDF, or fax with cover sheet, depending on payer preference.
How do I resolve a CARC 252 (CO-252) denial?
Start with the most common root cause: Claim was submitted without a required attachment (op note for unlisted codes, pathology for surgery, invoice for NOC drugs, ABN for non-covered service). First step: Rebill as a corrected claim (frequency 7) with the attachment properly flagged in the PWK segment; a formal appeal is rarely needed. See the full remediation and appeal checklist on this page before filing a formal appeal.
Is CARC 252 patient responsibility?
No — CARC 252 is typically carried under CO (Contractual Obligation) or OA (Other Adjustment), which means it is the provider's responsibility, not the patient's. Do not bill the patient unless the 835 CAS group code is PR.
What does CARC 252 look like on an EOB or 835 remittance?
On the 835 ERA, CARC 252 appears in Loop 2110 CAS segment as "CAS*CO*252*{amount}". On a paper EOB the same code prints in the Adjustment/Denial Reason column with the X12 description: "An attachment/other documentation is required to adjudicate this claim/service." — usually paired with one or more RARC remark codes in the same remittance line for additional context.
Which RARC is paired with CARC 252?
CARC 252 is commonly observed with RARC M127, N706, N26. The RARC narrows the reason — for example, pointing at a missing modifier, an LCD citation, or a specific policy. Fix the underlying CARC first; the RARC usually clears with the corrected claim.
Disclaimer
This page is operational reference for medical-billing professionals. It is not legal, clinical, or contractual advice. X12 code descriptors are maintained by the X12 External Code Lists; always verify against the current X12 release and the payer's own published policy before submitting or appealing a claim.