Denial Code Decoder
N522 — Duplicate of an already-processed claim
The payer matched this submission to a claim it has already processed. The companion to CO-18 — the work is reconciling against the original adjudication rather than resubmitting again.
Billable to the patient? No — the original adjudication governs any balance.
Where this denial is born
- Front desk
- Coding
- Claim build
- Submission
- Adjudication
This denial is usually created at the highlighted stage — that is where prevention lives.
Answer the questions — follow the path
The same questions an experienced biller asks, in order. Your answers draw the route to the right action.
Did the original claim pay correctly?
The full decision tree
Did the original claim pay correctly?
- Yes →
Post the original and close this one. Reconcile against the original remittance; no further submission.
- No →
Work the ORIGINAL claim's outcome. Whatever the original did — denied, underpaid — is the thing to work, via correction or appeal of that claim, not a fresh submission.
Prevention
Check claim status before resubmitting anything — most duplicates are impatience with a claim that was already in process.
Related reading
The code list, and when it was last checked
X12 maintains the Remittance Advice Remark Codes list, where this code is listed as N522. A remark code carries no adjustment group of its own — the group you see on the remittance line belongs to the reason code it arrived with. It has been on the list since November 1, 2009, and X12 last revised its entry on March 1, 2010.
Checked against the list revision dated July 1, 2026 on August 7, 2026, where it reads as an active code.
Sources
The paragraphs behind the guidance above. A page that tells you what to do about money should show you what the instruction rests on.
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