835 Denial Combination

CO-16+N479

CO

Contractual Obligation · Claim-Level Adjustment

Missing Information

What This Combination Means

The payer is denying payment because the claim lacks required Explanation of Benefits documentation from another insurer. This occurs when the claim is being processed as secondary or subsequent coverage, but the provider did not attach or submit the primary payer's EOB. The provider is contractually required to write off this amount unless the missing EOB is supplied.

Financial Responsibility

provider writeoff

The provider must write off the denied amount under contractual obligation (CO). The patient cannot be billed for this amount unless the claim is successfully corrected and reprocessed.

88%

Appeal Success

30-45 days (corrected claim submission)

Avg. Resolution

Medium

Difficulty

Yes

Appealable

Step-by-Step Resolution

Steps tailored specifically to this CO-16+N479 combination — not generic advice.

Appealable:This is appealable because it represents a correctable submission error (missing documentation) rather than a contracted fee-schedule adjustment.
  1. 1

    Obtain the primary or other payer's Explanation of Benefits for the date of service and patient in question

    The N479 specifically identifies that coordination of benefits documentation is missing; retrieve the EOB from the other insurance carrier or patient records

  2. 2

    Submit a corrected claim with the EOB attached per payer specifications

    Use frequency code 7 (replacement) or payer-specific corrected claim procedure, ensuring the EOB is included as an attachment or scanned document

  3. 3

    Track corrected claim through adjudication to verify reprocessing with the coordination of benefits information

    Monitor the claim status to confirm the payer processes it with the primary EOB information and reverses the CO-16 denial

Specialty Context

How CO-16+N479 typically presents across different practice types.

Dental

Common when dual dental coverage exists (e.g., patient has coverage through both their employer and spouse's employer); the secondary dental plan requires the primary plan's EOB before processing

Medical

Frequent with Medicare Secondary Payer situations, workers' compensation coordination, or patients with both group and individual coverage; requires primary payer's EOB to determine secondary responsibility

Behavioral Health

Occurs when behavioral health services are covered under multiple policies (e.g., Medicaid and private insurance, or EAP benefits exhausted and commercial insurance becomes primary); secondary payer needs primary EOB

Individual Code References

View the standalone definition for each code in this combination.

CARC 16RARC N479

Medicare Contractor Guidance for CARC 16

FCSO + Noridian + uhc + aetna + bcbs_az

This RUC is received when a claim is submitted with missing, incorrect, or invalid information. For details pertaining to your claim, please refer to the remittance advice remark codes (RARCs) on the remittance advice (RA).

How to Prevent CARC 16 Denials

  • ✓

    Review the RARC on the remittance advice to identify which specific field has the error.

  • ✓

    Per Medicare guidelines, claims must be filed no later than 12 months after the date of service. RUCs are not considered filed/submitted.

CMS guidelines for completion of form CMS-1500 in the Medicare Claims Processing Manual (100-04), Chapter 26SPOTFee Schedule Lookup ToolCMS laboratory demographics lookupModifier lookup toolNoridian Medicare PortalNMPIVRSame or SimilarPECOSPDAC

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Synthesized from official definitions — not from training data

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