Latency: <2ms Edge Availability: 99.99% Standard: ANSI 835 / WPC CARC Verified: Sep 2026 V8 Pure Compute

CARC 18 Denial Code (Exact Duplicate Claim/Service) | ANSI 835 EDI Spec

Q: What does CARC 18 mean on an 835 ERA?

CARC 18 signifies: "Exact duplicate claim/service.". It explains why the payer did not pay the full billed charge.

Q: How do medical billing teams resolve and appeal CARC 18?

Verify whether the earlier claim was already paid. If services were legitimately repeated on the same date, append modifier 76 (repeat procedure) or 59/XE and appeal.

Comprehensive healthcare EDI technical reference and denial resolution guide for Claim Adjustment Reason Code 18 (Exact Duplicate Claim/Service) under ANSI ASC X12 835 005010X221A1.

View Pricing & SLA → ⚡ Test in Live Workbench ← Back to Healthcare EDI ANSI X12 Parser API

Official Regulatory Standard & Verification Protocol Authority: Accredited Standards Committee X12 / HIPAA 5010 ↗

Direct Answer Capsule: Comprehensive healthcare EDI technical reference and denial resolution guide for Claim Adjustment Reason Code 18 (Exact Duplicate Claim/Service) under ANSI ASC X12 835 005010X221A1. Conforms strictly to ANSI ASC X12 Standards (005010) with zero cold-starts and deterministic edge verification.

Execution SLA

<2ms Edge (Cloudflare V8)

Governing Norm

ANSI 835 / WPC CARC

Active Standard

Sep 2026 Edition

Throughput Limit

512 KB / Payload

Data Privacy

100% In-Memory (Zero Store)

Interactive Edge Workbench

⚡ Live CARC 18 Denial Code (Exact Duplicate Claim/Service) | ANSI 835 EDI Spec Interactive Workbench

Test real-time validation and deterministic schema parsing for CARC 18 Denial Code (Exact Duplicate Claim/Service) | ANSI 835 EDI Spec directly in your browser. Sub-5ms Cloudflare edge execution with zero setup.

32KB Demo Cap 60 req/min Burst <2ms V8 Compute Zero Data Retention

input.x12 0 B

output.json demo-ready

Status: Ready

{
  "status": "Click 'Run Edge Parse' to test live on Global Edge Isolates..."
}

Specification & Structural Breakdown

Technical Rule Summary: Implementation conforms strictly to ANSI ASC X12 Standards (005010). Data ingestion is fully deterministic: identical inputs always produce bit-for-bit identical outputs without ambient side-effects.

Claim Adjustment Reason Code (CARC) 18 communicates: "Exact duplicate claim/service.".

In ANSI X12 835 Electronic Remittance Advice (ERA) files, CARC 18 is reported in Loop 2110 (Service Payment Information) or Loop 2100 (Claim Payment Information) under the Claim Adjustment (CAS) segment with Group Code 'OA' (Other Adjustment), formatted as: CAS*OA*18*AMOUNT~.

Root Cause: A claim with the same patient, provider, date of service, procedure code, and billed amount was previously received and adjudicated.

Adjudication & Appeal Strategy: Verify whether the earlier claim was already paid. If services were legitimately repeated on the same date, append modifier 76 (repeat procedure) or 59/XE and appeal.

Attribute	Value	Technical Guidance
Reason Code	CARC 18	Exact Duplicate Claim/Service
Standard Group Code	OA	Other Adjustment
ANSI 835 Segment	CASOA18*AMOUNT~	Loop 2110 or Loop 2100
Balance Billing Patient	Prohibited.	Compliance with billing regulations
Common RARCs	N522, MA01	Remittance Advice Remark Codes
Recommended Action	Verify whether the earlier claim was already paid. If services were legitimately repeated on the same date, append modifier 76 (repeat procedure) or 59/XE and appeal.	Workflow for billing teams

Parsed JSON Response Model

The edge microservice transforms input payloads into strongly-typed hierarchical JSON envelopes with sub-5ms latency:

HTTP 200 JSON Response Envelope

{
  "transactionType": "835",
  "claimNumber": "CLM-2026-001",
  "adjudication": {
    "billedAmount": 500,
    "paidAmount": 0,
    "adjustments": [
      {
        "groupCode": "OA",
        "groupName": "Other Adjustment",
        "reasonCode": "18",
        "reasonDescription": "Exact Duplicate Claim/Service",
        "adjustmentAmount": 500
      }
    ]
  }
}

Copy-Paste Integration Code (5 Languages)

Integrate CARC 18 Denial Code (Exact Duplicate Claim/Service) | ANSI 835 EDI Spec directly into your production application with native, zero-dependency code snippets in cURL, Node.js, Python, Go, and C#:

curl --request POST \
  --url "https://healthcare-edi-ansi-x12-parser-837p-835-271.stanzaapi.com/api/v1/x12/parse" \
  --header "Content-Type: application/json" \
  --header "x-api-key: YOUR_API_KEY" \
  --data '{
  "raw": "ISA*00*          *00*          *ZZ*SUBMITTER1     *ZZ*RECEIVER01     *260830*1200*^*00501*000000001*0*P*:~GS*HC*SENDER*RECEIVER*20260830*1200*1*X*005010X222A1~ST*837*0001*005010X222A1~BHT*0019*00*CLAIM001*20260830*1200*CH~NM1*41*2*DR DOE CLINIC*****46*1234567890~PER*IC*SUPPORT*TE*8005551212~HL*1**20*1~NM1*85*2*DR DOE CLINIC*****XX*1992837465~HL*2*1*22*0~NM1*IL*1*SMITH*JANE****MI*W123456780~CLM*CLM001*150.00***11::1*Y*A*Y*Y~LX*1~SV1*HC:99213*150.00*UN*1***1~SE*11*0001~GE*1*1~IEA*1*000000001~"
}'

const response = await fetch("https://healthcare-edi-ansi-x12-parser-837p-835-271.stanzaapi.com/api/v1/x12/parse", {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
    "x-api-key": process.env.API_KEY || "YOUR_API_KEY"
  },
  body: JSON.stringify({
  "raw": "ISA*00*          *00*          *ZZ*SUBMITTER1     *ZZ*RECEIVER01     *260830*1200*^*00501*000000001*0*P*:~GS*HC*SENDER*RECEIVER*20260830*1200*1*X*005010X222A1~ST*837*0001*005010X222A1~BHT*0019*00*CLAIM001*20260830*1200*CH~NM1*41*2*DR DOE CLINIC*****46*1234567890~PER*IC*SUPPORT*TE*8005551212~HL*1**20*1~NM1*85*2*DR DOE CLINIC*****XX*1992837465~HL*2*1*22*0~NM1*IL*1*SMITH*JANE****MI*W123456780~CLM*CLM001*150.00***11::1*Y*A*Y*Y~LX*1~SV1*HC:99213*150.00*UN*1***1~SE*11*0001~GE*1*1~IEA*1*000000001~"
})
});

const data = await response.json();
console.log(data);

import requests
import json

url = "https://healthcare-edi-ansi-x12-parser-837p-835-271.stanzaapi.com/api/v1/x12/parse"
headers = {
    "Content-Type": "application/json",
    "x-api-key": "YOUR_API_KEY"
}
payload = {
    "raw": "ISA*00*          *00*          *ZZ*SUBMITTER1     *ZZ*RECEIVER01     *260830*1200*^*00501*000000001*0*P*:~GS*HC*SENDER*RECEIVER*20260830*1200*1*X*005010X222A1~ST*837*0001*005010X222A1~BHT*0019*00*CLAIM001*20260830*1200*CH~NM1*41*2*DR DOE CLINIC*****46*1234567890~PER*IC*SUPPORT*TE*8005551212~HL*1**20*1~NM1*85*2*DR DOE CLINIC*****XX*1992837465~HL*2*1*22*0~NM1*IL*1*SMITH*JANE****MI*W123456780~CLM*CLM001*150.00***11::1*Y*A*Y*Y~LX*1~SV1*HC:99213*150.00*UN*1***1~SE*11*0001~GE*1*1~IEA*1*000000001~"
}

response = requests.post(url, json=payload, headers=headers)
print(response.json())

package main

import (
	"bytes"
	"fmt"
	"io"
	"net/http"
	"os"
)

func main() {
	url := "https://healthcare-edi-ansi-x12-parser-837p-835-271.stanzaapi.com/api/v1/x12/parse"
	payload := []byte(`{"raw":"ISA*00*          *00*          *ZZ*SUBMITTER1     *ZZ*RECEIVER01     *260830*1200*^*00501*000000001*0*P*:~GS*HC*SENDER*RECEIVER*20260830*1200*1*X*005010X222A1~ST*837*0001*005010X222A1~BHT*0019*00*CLAIM001*20260830*1200*CH~NM1*41*2*DR DOE CLINIC*****46*1234567890~PER*IC*SUPPORT*TE*8005551212~HL*1**20*1~NM1*85*2*DR DOE CLINIC*****XX*1992837465~HL*2*1*22*0~NM1*IL*1*SMITH*JANE****MI*W123456780~CLM*CLM001*150.00***11::1*Y*A*Y*Y~LX*1~SV1*HC:99213*150.00*UN*1***1~SE*11*0001~GE*1*1~IEA*1*000000001~"}`)

	req, _ := http.NewRequest("POST", url, bytes.NewBuffer(payload))
	req.Header.Add("Content-Type", "application/json")
	req.Header.Add("x-api-key", os.Getenv("API_KEY"))

	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)
	fmt.Println(string(body))
}

using System;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;

class Program
{
    static async Task Main()
    {
        using var client = new HttpClient();
        client.DefaultRequestHeaders.Add("x-api-key", Environment.GetEnvironmentVariable("API_KEY") ?? "YOUR_API_KEY");

        var json = @"{""raw"":""ISA*00*          *00*          *ZZ*SUBMITTER1     *ZZ*RECEIVER01     *260830*1200*^*00501*000000001*0*P*:~GS*HC*SENDER*RECEIVER*20260830*1200*1*X*005010X222A1~ST*837*0001*005010X222A1~BHT*0019*00*CLAIM001*20260830*1200*CH~NM1*41*2*DR DOE CLINIC*****46*1234567890~PER*IC*SUPPORT*TE*8005551212~HL*1**20*1~NM1*85*2*DR DOE CLINIC*****XX*1992837465~HL*2*1*22*0~NM1*IL*1*SMITH*JANE****MI*W123456780~CLM*CLM001*150.00***11::1*Y*A*Y*Y~LX*1~SV1*HC:99213*150.00*UN*1***1~SE*11*0001~GE*1*1~IEA*1*000000001~""}";
        var payload = new StringContent(json, Encoding.UTF8, "application/json");

        var response = await client.PostAsync("https://healthcare-edi-ansi-x12-parser-837p-835-271.stanzaapi.com/api/v1/x12/parse", payload);
        var content = await response.Content.ReadAsStringAsync();
        Console.WriteLine(content);
    }
}

Frequently Asked Questions & Technical Notes

What does CARC 18 mean on an 835 ERA?

CARC 18 signifies: "Exact duplicate claim/service.". It explains why the payer did not pay the full billed charge.

Can a provider balance-bill the patient for CARC 18?

Prohibited.

How do medical billing teams resolve and appeal CARC 18?

Verify whether the earlier claim was already paid. If services were legitimately repeated on the same date, append modifier 76 (repeat procedure) or 59/XE and appeal.

Related Healthcare EDI ANSI X12 Parser API Formats

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CARC 18 Denial Code (Exact Duplicate Claim/Service) | ANSI 835 EDI Spec

⚡ Live CARC 18 Denial Code (Exact Duplicate Claim/Service) | ANSI 835 EDI Spec Interactive Workbench

Specification & Structural Breakdown

Parsed JSON Response Model

Copy-Paste Integration Code (5 Languages)

Frequently Asked Questions & Technical Notes

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