CARC 18Duplicate Appealable

Exact duplicate claim/service

Q: Is CARC 18 appealable?

Yes, CARC 18 is appealable with an estimated win rate of approximately 90.00%.

Quick Action: Verify original claim status; if corrected claim, resubmit with frequency code 7.

Typically seen with:CO — Contractual ObligationOA — Other Adjustment

~90.00%

Estimated appeal win rate for CARC 18 denials

What Does CARC 18 Mean?

CARC 18 — "Exact duplicate claim/service" — is a Claim Adjustment Reason Code used by payers to indicate why a claim or service line was adjusted. This code falls under the Duplicate category.

Common Causes

Here are the most common reasons this denial code appears on your remittance advice:

Same claim submitted more than once (system error or manual re-entry)
Corrected claim sent without frequency code 7 (replacement) indicator
Clearinghouse re-transmitted the claim due to transmission errors
Original claim was processed but payment not yet reflected in the system
Multiple staff members submitted the same claim independently

Is CARC 18 Appealable?

Yes, CARC 18 is appealable. With proper documentation and a well-crafted appeal, this denial code has an estimated win rate of approximately 90.00%. This is one of the higher-success-rate denial codes — prioritize these appeals.

How to Appeal CARC 18

Follow these steps to maximize your chances of a successful appeal:

1 Check if the original claim was already paid — review ERA/835 data

2 If this is a legitimate corrected claim, resubmit with frequency code 7

3 If the original was denied and this is a resubmission, include the original claim reference number

4 Contact the payer to verify the status of the original claim

5 If truly not a duplicate, appeal with documentation showing distinct services

Related RARC Codes

These Remittance Advice Remark Codes are commonly paired with CARC 18. The RARC tells you the specific reason for the adjustment.

MA04 Secondary payment cannot be considered without the identity of or payment information from the primary payer

N30 Patient ineligible for this service

N362 The number of Days or Units of Service exceeds our acceptable maximum

Appeal Letter Template

.DOCX

Customize the fields below to generate a ready-to-send appeal letter for CARC 18. Downloads as a formatted Word document.

Practice/Organization

Payer Name

Claim Number

Patient Name

Member ID

Date of Service

Denied Amount

Provider Name

NPI

Phone

Letter Body (editable)

[Date]
[Payer Name]
[Payer Address]

RE: Appeal for Claim #[Claim Number]
Patient: [Patient Name] | Member ID: [Member ID]
Date of Service: [Date of Service] | Denied Amount: $[Denied Amount]

Dear Claims Review Department,

I am writing to formally appeal the denial of the above-referenced claim, denied with CARC 18: "Exact duplicate claim/service".

Our appeal is based on the following:

- Check if the original claim was already paid — review ERA/835 data
- If this is a legitimate corrected claim, resubmit with frequency code 7
- If the original was denied and this is a resubmission, include the original claim reference number
- Contact the payer to verify the status of the original claim
- If truly not a duplicate, appeal with documentation showing distinct services

We have reviewed the common reasons for this denial and can confirm that the following do not apply to this claim:

- Same claim submitted more than once (system error or manual re-entry)
- Corrected claim sent without frequency code 7 (replacement) indicator
- Clearinghouse re-transmitted the claim due to transmission errors
- Original claim was processed but payment not yet reflected in the system
- Multiple staff members submitted the same claim independently

Recommended action: Verify original claim status; if corrected claim, resubmit with frequency code 7.

Enclosed please find supporting documentation for your review. We respectfully request reconsideration and payment of $[Denied Amount].

Sincerely,
[Provider Name]
[NPI] | [Phone]
[Practice/Organization Name]

Letter Preview

This is how your letter will look when downloaded

March 26, 2026

[Payer Name]

[Payer Address]

RE: Appeal for Claim #[Claim Number]

Patient: [Patient Name] | Member ID: [Member ID]

Date of Service: [Date of Service] | Denied Amount: $[Denied Amount]

Dear Claims Review Department,

I am writing to formally appeal the denial of the above-referenced claim, denied with CARC 18: "Exact duplicate claim/service".

Our appeal is based on the following:

Check if the original claim was already paid — review ERA/835 data
If this is a legitimate corrected claim, resubmit with frequency code 7
If the original was denied and this is a resubmission, include the original claim reference number
Contact the payer to verify the status of the original claim
If truly not a duplicate, appeal with documentation showing distinct services

We have reviewed the common reasons for this denial and can confirm that the following do not apply to this claim:

Same claim submitted more than once (system error or manual re-entry)
Corrected claim sent without frequency code 7 (replacement) indicator
Clearinghouse re-transmitted the claim due to transmission errors
Original claim was processed but payment not yet reflected in the system
Multiple staff members submitted the same claim independently

Recommended action: Verify original claim status; if corrected claim, resubmit with frequency code 7.

Enclosed please find supporting documentation for your review. We respectfully request reconsideration and payment of $[Denied Amount].

Sincerely,

[Provider Name]

[NPI] | [Phone]

[Practice/Organization Name]

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