Official X12 description
“The attachment/other documentation that was received was incomplete or deficient.”
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 251 actually means
CARC 251 is the 'bad attachment' counterpart to CARC 163: you sent documentation but the payer found it incomplete — missing signature, missing DOS, wrong patient, missing required element (vital signs, time units, etc.). Fix the deficiency and resubmit.
Common root causes
- Clinical note missing signature, date, or credentials.
- Attachment for the wrong patient or DOS.
- Required element (pre-op H&P, orders, time log) not included.
Prevention checklist
- Pre-submission QC of every attachment against a payer-aligned checklist.
- EHR macros that include all required elements before release for billing.
Appeal strategy — step by step
Most CARC 251 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.
- 1Resubmit with the corrected, complete attachment within the plan's attachment-response window.
Sample appeal-letter language for CARC 251
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 251 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 251?
Out of 306 seeded CARCs, ranked by combined US monthly search volume for "CARC 251", "CO-251 denial", and "denial code 251".
Platform frequency ranks publish once the anonymized denial-rate pipeline reaches the publication threshold (strategy §12 Phase 2).
How QuickRCM prevents CARC 251
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 251
Under the CAQH CORE Payment and Remittance Uniform Use rule, health plans may pair CARC 251 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 |
|---|---|---|---|
| M42 | The medical necessity form must be personally signed by the attending physician. | CO or PI | 1 |
| M135 | Missing/incomplete/invalid plan of treatment. | 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 |
| MA75 | Missing/incomplete/invalid patient or authorized representative signature. | 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 |
| MA111 | Missing/incomplete/invalid purchase price of the test(s) and/or the performing laboratory's name and address. | CO or PI | 1 |
| N4 | Missing/Incomplete/Invalid prior Insurance Carrier(s) EOB. | CO or PI | 1 |
| N28 | Consent form requirements not fulfilled. | CO or PI | 1 |
| N78 | The necessary components of the child and teen checkup (EPSDT) were not completed. | CO or PI | 1 |
| N80 | Missing/incomplete/invalid prenatal screening information. | CO or PI | 1 |
| N170 | A new/revised/renewed certificate of medical necessity is needed. | CO or PI | 1 |
| N205 | Information provided was illegible. | CO or PI | 1 |
| N214 | Missing/incomplete/invalid history of the related initial surgical procedure(s). | CO or PI | 1 |
| N222 | Incomplete/invalid Admitting History and Physical report. | CO or PI | 1 |
| N224 | Incomplete/invalid documentation of benefit to the patient during initial treatment period. | CO or PI | 1 |
| N226 | Incomplete/invalid American Diabetes Association Certificate of Recognition. | CO or PI | 1 |
| N227 | Incomplete/invalid Certificate of Medical Necessity. | CO or PI | 1 |
| N228 | Incomplete/invalid consent form. | CO or PI | 1 |
| N231 | Incomplete/invalid invoice or statement certifying the actual cost of the lens, less discounts, and/or the type of intraocular lens used. | CO or PI | 1 |
| N232 | Incomplete/invalid itemized bill/statement. | CO or PI | 1 |
| N233 | Incomplete/invalid operative note/report. | CO or PI | 1 |
| N234 | Incomplete/invalid oxygen certification/re‐certification. | CO or PI | 1 |
| N235 | Incomplete/invalid pacemaker registration form. | CO or PI | 1 |
| N236 | Incomplete/invalid pathology report. | CO or PI | 1 |
| N237 | Incomplete/invalid patient medical record for this service. | CO or PI | 1 |
| N238 | Incomplete/invalid physician certified plan of care. | CO or PI | 1 |
| N239 | Incomplete/invalid physician financial relationship form. | CO or PI | 1 |
| N240 | Incomplete/invalid radiology report. | CO or PI | 1 |
| N241 | Incomplete/invalid review organization approval. | CO or PI | 1 |
| N242 | Incomplete/invalid radiology film(s)/image(s). | CO or PI | 1 |
| N243 | Incomplete/invalid/not approved screening document. | CO or PI | 1 |
| N244 | Incomplete/Invalid pre-operative images/visual field results. | CO or PI | 1 |
| N245 | Incomplete/invalid plan information for other insurance. | CO or PI | 1 |
| N331 | Missing/incomplete/invalid physician order date. | CO or PI | 1 |
| N354 | Incomplete/invalid invoice. | CO or PI | 1 |
| N375 | Missing/incomplete/invalid questionnaire/information required to determine dependent eligibility. | CO or PI | 1 |
| N392 | Incomplete/invalid emergency department records. | CO or PI | 1 |
| N394 | Incomplete/invalid progress notes/report. | CO or PI | 1 |
| N396 | Incomplete/invalid laboratory report. | CO or PI | 1 |
| N399 | Incomplete/invalid elective consent form. | CO or PI | 1 |
| N402 | Incomplete/invalid periodontal charting. | CO or PI | 1 |
| N404 | Incomplete/invalid facility certification. | CO or PI | 1 |
| N440 | Incomplete/invalid anesthesia physical status report/indicators. | CO or PI | 1 |
| N446 | Incomplete/invalid document for actual cost or paid amount. | CO or PI | 1 |
| N452 | Incomplete/invalid Admission Summary Report. | CO or PI | 1 |
| N454 | Incomplete/invalid Consultation Report. | CO or PI | 1 |
| N456 | Incomplete/invalid Physician Order. | CO or PI | 1 |
| N458 | Incomplete/invalid Diagnostic Report. | CO or PI | 1 |
| N460 | Incomplete/invalid Discharge Summary. | CO or PI | 1 |
| N462 | Incomplete/invalid Nursing Notes. | CO or PI | 1 |
| N466 | Incomplete/invalid Physical Therapy Notes/Report. | CO or PI | 1 |
| N468 | Incomplete/invalid Report of Tests and Analysis Report. | CO or PI | 1 |
| N474 | Incomplete/invalid certification. | CO or PI | 1 |
| N476 | Incomplete/invalid completed referral form. | CO or PI | 1 |
| N478 | Incomplete/invalid Dental Models. | CO or PI | 1 |
| N480 | Incomplete/invalid Explanation of Benefits (Coordination of Benefits or Medicare Secondary Payer). | CO or PI | 1 |
| N482 | Incomplete/invalid Models. | CO or PI | 1 |
| N486 | Incomplete/invalid Physical Therapy Certification. | CO or PI | 1 |
| N488 | Incomplete/invalid Prosthetics or Orthotics Certification. | CO or PI | 1 |
| N490 | Incomplete/invalid referral form. | CO or PI | 1 |
| N491 | Missing/Incomplete/Invalid Exclusionary Rider Condition. | CO or PI | 1 |
| N494 | Incomplete/invalid Doctor First Report of Injury. | CO or PI | 1 |
| N496 | Incomplete/invalid Supplemental Medical Report. | CO or PI | 1 |
| N498 | Incomplete/invalid Medical Permanent Impairment or Disability Report. | CO or PI | 1 |
| N500 | Incomplete/invalid Medical Legal Report. | CO or PI | 1 |
| N502 | Incomplete/invalid Vocational Report. | CO or PI | 1 |
| N504 | Incomplete/invalid Work Status Report. | CO or PI | 1 |
| N543 | Incomplete/invalid income verification. | CO or PI | 1 |
| N556 | Incomplete/invalid medication list. | CO or PI | 1 |
| N570 | Missing/incomplete/invalid credentialing data. | CO or PI | 1 |
| N668 | Incomplete/invalid prescription. | CO or PI | 1 |
| N679 | Incomplete/Invalid 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 |
| N686 | Missing/incomplete/Invalid questionnaire needed to complete payment determination. | CO or PI | 1 |
| N705 | Incomplete/invalid documentation. | CO or PI | 1 |
| N707 | Incomplete/invalid orders. | CO or PI | 1 |
| N709 | Incomplete/invalid notes. | CO or PI | 1 |
| N711 | Incomplete/invalid summary. | CO or PI | 1 |
| N713 | Incomplete/invalid report. | CO or PI | 1 |
| N715 | Incomplete/invalid chart. | CO or PI | 1 |
| N717 | Incomplete/Invalid documentation of face-to-face examination. | CO or PI | 1 |
| N730 | Incomplete/invalid patient medical/dental record for this service. | CO or PI | 1 |
| N731 | Incomplete/Invalid mental health assessment. | CO or PI | 1 |
| N736 | Incomplete/invalid Sleep Study Report. | CO or PI | 1 |
| N738 | Incomplete/invalid Vein Study Report. | CO or PI | 1 |
| N746 | Incomplete/invalid Ambulance Report. | CO or PI | 1 |
| N750 | Incomplete/invalid Blood Gas Report. | CO or PI | 1 |
| N764 | Missing/incomplete/invalid Hematocrit (HCT) value. | CO or PI | 1 |
| N768 | Incomplete/invalid initial evaluation report. | CO or PI | 1 |
| N792 | Incomplete/invalid history & physical report. | CO or PI | 1 |
| N796 | Missing/incomplete/invalid Hemoglobin (Hb or Hgb) value. | 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 |
| N901 | Incomplete/Invalid Therapy Notes/Report. | CO or PI | 1 |
| N903 | Incomplete/Invalid Health Risk Assessment (HRA). | CO or PI | 1 |
Frequently asked questions — CARC 251
What does CARC 251 mean?
CARC 251 is an X12 Claim Adjustment Reason Code. The official definition is: "The attachment/other documentation that was received was incomplete or deficient." In plain English, the payer is telling you cARC 251 is the 'bad attachment' counterpart to CARC 163: you sent documentation but the payer found it incomplete — missing signature, missing DOS, wrong patient, missing required element (vital signs, time units, etc.). Fix the deficiency and resubmit.
How do I resolve a CARC 251 (CO-251) denial?
Start with the most common root cause: Clinical note missing signature, date, or credentials. First step: Resubmit with the corrected, complete attachment within the plan's attachment-response window. See the full remediation and appeal checklist on this page before filing a formal appeal.
Is CARC 251 patient responsibility?
No — CARC 251 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 251 look like on an EOB or 835 remittance?
On the 835 ERA, CARC 251 appears in Loop 2110 CAS segment as "CAS*CO*251*{amount}". On a paper EOB the same code prints in the Adjustment/Denial Reason column with the X12 description: "The attachment/other documentation that was received was incomplete or deficient." — usually paired with one or more RARC remark codes in the same remittance line for additional context.
Which RARC is paired with CARC 251?
CARC 251 is commonly observed with RARC M127, N706. 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.