CARC 18: Exact duplicate claim/service.
The carrier sees this as a duplicate of a claim already processed. Check whether the original was paid, denied, or rejected — your action depends on which.
CARC 18 appears on the 835 ERA (Electronic Remittance Advice) that the payer returns after claim adjudication. It explains a reduction, denial, or payment adjustment to your billing team. For your practice, the question is workflow: identify the pattern, route the denial to the right resolution path (rebill, appeal, write-off), and recover what's recoverable without burning RVU time on dead-end fights.
What CARC 18 means
The official X12 description is: “Exact duplicate claim/service.”
In plain language: The carrier sees this as a duplicate of a claim already processed. Check whether the original was paid, denied, or rejected — your action depends on which.
Common scenarios
- Provider re-submitted accidentally
- Date-of-service repeated
- Same CPT same day
Practice workflow for CARC X 18
Look up the original claim. If paid, the duplicate denial is correct — no action. If the original was denied, appeal that original (not the duplicate). If submitted in error, no action needed.
CARC 18 group codes explained
On the 835 ERA, CARC 18 appears alongside a group code that signals who is financially responsible for the adjustment. CO (Contractual Obligation) — Contractual write-off. The provider agreed to the rate. Patient does NOT owe this amount.
Frequently asked questions
What does CARC 18 mean?
Exact duplicate claim/service. In plain language: The carrier sees this as a duplicate of a claim already processed. Check whether the original was paid, denied, or rejected — your action depends on which.
Is CARC 18 appealable?
CARC 18 is usually not appealable on its own — it's typically a contractual, informational, or routine adjustment. Look up the original claim. If paid, the duplicate denial is correct — no action. If the original was denied, appeal that original (not the duplicate). If submitted in error, no action needed.
Which group code does CARC 18 appear under?
CARC 18 most often appears under: CO (Contractual Obligation) — Contractual write-off. The provider agreed to the rate. Patient does NOT owe this amount.
When does CARC 18 typically appear on a denial?
Common scenarios: Provider re-submitted accidentally; Date-of-service repeated; Same CPT same day.
What should I do if I see CARC 18 on the 835?
Look up the original claim. If paid, the duplicate denial is correct — no action. If the original was denied, appeal that original (not the duplicate). If submitted in error, no action needed.
Related resources
Sources
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