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N479 Remark Code: Missing EOB for COB or MSP Claim

N479 means the payer is processing the claim as secondary (through coordination of benefits or Medicare Secondary Payer rules) and needs the primary payer's explanation of benefits, which was not included. Attach the EOB or send the prior payer's adjudication data and refile.

Quick facts

Code
N479 (RARC N479)
Status
Active In use since July 1, 2008.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The claim was denied or held until the primary payer's EOB is supplied. The provider can correct this, so the amount is not patient responsibility.
  • OA (Other Adjustment): Some payers report the missing coordination of benefits information as an other adjustment. It is still a request for the primary payer's results.
Official description
Missing Explanation of Benefits (Coordination of Benefits or Medicare Secondary Payer).
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N479 means

Before a secondary payer can calculate what it owes, it has to know what the primary payer allowed, paid, and assigned to the patient. The explanation of benefits (EOB) or remittance from the primary is the proof. N479 says that proof was missing from the claim.

The official wording covers two situations: ordinary coordination of benefits (COB) between two commercial or government plans, and Medicare Secondary Payer (MSP) cases where another coverage pays before Medicare. In both, the remark is a request, not a decision on coverage.

Common causes

  • The secondary claim was sent before the primary payer finished processing.
  • The claim went out electronically without the other-payer paid amounts and adjustment codes.
  • A paper claim listed other insurance in box 9 or 11d but no EOB was attached.
  • The practice did not know another plan was primary, so the claim was billed as if the secondary plan were the only coverage.

How to fix it

  1. Confirm payer order with both plans and the patient. See eligibility and COB denials for common order-of-benefits issues.
  2. Get the primary’s remittance for the same dates of service and lines.
  3. Refile the secondary claim with the primary’s paid amount, allowed amount, and adjustment reason codes, or attach the EOB if the payer requires paper.
  4. Use the correct resubmission path. If the original claim was denied and the payer accepts replacements, use resubmission code 7 in box 22 with the original claim number. Otherwise follow its instructions.
  5. Watch filing limits. Secondary claims have their own deadlines, often counted from the primary’s payment date.

How to prevent it

Collect all coverage at registration and ask about other insurance at every visit. Hold secondary claims in a queue until the primary remittance posts, and send the primary’s adjudication data automatically with the crossover or secondary claim.

Codes that may appear with N479

  • OA-22 (This care may be covered by another payer per coordination of benefits.): The payer believes another plan is primary and needs that plan's results first.
  • CO-252 (An attachment/other documentation is required to adjudicate this claim/service.): A required attachment is missing; N479 names it as the prior payer's EOB.
  • CO-16 (Claim/service lacks information or has submission/billing error(s).): General missing-information reason used by some payers with this remark.
  • N4 (Missing/Incomplete/Invalid prior Insurance Carrier(s)): A broader remark for a missing, incomplete, or invalid EOB from a prior insurance carrier.
  • N480 (Incomplete/invalid Explanation of Benefits (Coordination of Benefits or Medicare Secondary Payer).): The EOB arrived but was incomplete or invalid.
  • MA04 (Secondary payment cannot be considered without the identity of or payment information from the primary payer.): Medicare cannot consider secondary payment without the primary payer's identity or payment details.
  • MA64 (Our records indicate that we should be the third payer for this claim.): Medicare expects to be the third payer and needs results from both earlier payers.

N479 FAQ

Where does the primary EOB information go on a CMS-1500?

Other insurance details go in boxes 9 through 9d and 11d. The primary payer's EOB itself is usually attached or its payment and adjustment amounts are reported electronically, depending on the secondary payer's rules.

What if the primary payer denied the service?

Send the denial EOB. The secondary payer needs to see how the primary processed the service, whether it paid, applied cost-sharing, or denied it.

Why does the code mention Medicare Secondary Payer?

When an employer plan, liability insurer, or other coverage is primary to Medicare, Medicare acts as the secondary payer and needs the primary's EOB to calculate its payment.