How do I resolve a CO-18+N522 denial?

Before rebilling any claim, review the Noridian Medicare Portal in Claim inquiry for status of initial claim to avoid another denial If claim has denied previously, resolve claim denial by reviewing reason and remark code on claim specific remittance advice and follow the Denial Code Resolution steps for that reason and remark code A redetermination request may be submitted with all relevant supporting documentation. Review applicable Local Coverage Determination (LCD), LCD Policy Article, and documentation prior to submitting request. Noridian encourages redeterminations be submitted using the Noridian Medicare Portal If a supplier feels a claim denied duplicate in error, contact Telephone Reopenings

Can I appeal a CO-18+N522 denial?

CO-18+N522 denials are generally not appealable. Duplicate claim has already been submitted and processed

835 Denial Combination

CO-18+N522

Contractual Obligation · Service-Line Level Adjustment

What This Combination Means

Duplicate claim has already been submitted and processed

N/A

Appeal Success

7-14 days

Avg. Resolution

Medium

Difficulty

Appealable

Step-by-Step Resolution

Steps tailored specifically to this CO-18+N522 combination — not generic advice.

1
Before rebilling any claim, review the Noridian Medicare Portal in Claim inquiry for status of initial claim to avoid another denial
2
If claim has denied previously, resolve claim denial by reviewing reason and remark code on claim specific remittance advice and follow the Denial Code Resolution steps for that reason and remark code
3
A redetermination request may be submitted with all relevant supporting documentation. Review applicable Local Coverage Determination (LCD), LCD Policy Article, and documentation prior to submitting request. Noridian encourages redeterminations be submitted using the Noridian Medicare Portal
4
If a supplier feels a claim denied duplicate in error, contact Telephone Reopenings

Specialty Context

How CO-18+N522 typically presents across different practice types.

Dental

Medical

Behavioral Health

Individual Code References

View the standalone definition for each code in this combination.

CARC 18 RARC N522

Medicare Contractor Guidance for CARC 18

FCSO + Noridian + uhc + aetna + bcbs_az

You will receive this reason code when more than one claim has been submitted for the same item or service(s) provided to the same beneficiary on the same date(s) of service. OA18 = Exact duplicate claim or service.

How to Prevent CARC 18 Denials

✓
Before resubmitting a claim, check claims status via the SPOT or the Part B interactive voice response (IVR) system.
✓
Ensure necessary appropriate modifiers are appended to claim lines, if applicable, and resubmit the claim.
✓
Append the applicable modifier(s) to the procedure code even if the diagnosis indicates the exact site of the procedure.
✓
Do not resubmit an entire claim when partial payment made; when appropriate, resubmit denied lines only.
✓
Do not refile a claim if the total approved amount has been applied to the patient's deductible.

CMS IOM Pub. 100-04 Medicare Claims Processing Manual, Chapter 1, section 120SPOTIVRNoridian Medicare Portal

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