# CARC 252 Denial Code (Attachment / Documentation Required to Adjudicate) | ANSI 835 EDI Spec
> Comprehensive healthcare EDI technical reference and denial resolution guide for Claim Adjustment Reason Code 252 (Attachment / Documentation Required to Adjudicate) under ANSI ASC X12 835 005010X221A1.

- **Canonical URL:** https://stanzaapi.com/tools/x12-parser/carc/carc-252-attachment-required
- **Governing Standard:** ANSI ASC X12 Standards (005010) (Accredited Standards Committee X12 / HIPAA 5010)
- **Edge Latency SLA:** <2ms Edge (Cloudflare V8 Isolates)
- **Execution Model:** Pure compute $f(x) = y$, 100% In-Memory (Zero Store, Zero Log)

## Technical Overview & Governing Rules
Claim Adjustment Reason Code (CARC) 252 communicates: "An attachment/other documentation is required to adjudicate this claim/service.".

In ANSI X12 835 Electronic Remittance Advice (ERA) files, CARC 252 is reported in Loop 2110 (Service Payment Information) or Loop 2100 (Claim Payment Information) under the Claim Adjustment (CAS) segment with Group Code 'CO' (Contractual Obligation), formatted as: CAS*CO*252*AMOUNT~.

Root Cause: Complex surgical, unlisted code, or high-cost therapy where payer requires operative note, lab results, or invoice before payment.

Adjudication & Appeal Strategy: Submit requested clinical records via payer electronic attachment portal or PWK segment on resubmitted 837.

## Specification Matrix
| Attribute | Value | Technical Guidance |
| --- | --- | --- |
| Reason Code | CARC 252 | Attachment / Documentation Required to Adjudicate |
| Standard Group Code | CO | Contractual Obligation |
| ANSI 835 Segment | CAS*CO*252*AMOUNT~ | Loop 2110 or Loop 2100 |
| Balance Billing Patient | Prohibited. | Compliance with billing regulations |
| Common RARCs | N29, N650 | Remittance Advice Remark Codes |
| Recommended Action | Submit requested clinical records via payer electronic attachment portal or PWK segment on resubmitted 837. | Workflow for billing teams |

## Standard JSON Response Model
```json
{
  "transactionType": "835",
  "claimNumber": "CLM-2026-001",
  "adjudication": {
    "billedAmount": 500,
    "paidAmount": 0,
    "adjustments": [
      {
        "groupCode": "CO",
        "groupName": "Contractual Obligation",
        "reasonCode": "252",
        "reasonDescription": "Attachment / Documentation Required to Adjudicate",
        "adjustmentAmount": 500
      }
    ]
  }
}
```

## Frequently Asked Questions & Edge Cases
### Q: What does CARC 252 mean on an 835 ERA?
**A:** CARC 252 signifies: "An attachment/other documentation is required to adjudicate this claim/service.". It explains why the payer did not pay the full billed charge.

### Q: Can a provider balance-bill the patient for CARC 252?
**A:** Prohibited.

### Q: How do medical billing teams resolve and appeal CARC 252?
**A:** Submit requested clinical records via payer electronic attachment portal or PWK segment on resubmitted 837.