RARC N479: Missing EOB for COB or MSP Claim
The primary payer's Explanation of Benefits is missing from this secondary or COB claim — obtain the primary EOB, attach it, and resubmit to the secondary payer.
What Does RARC N479 Mean?
RARC N479 indicates that the claim submitted to a secondary payer is missing the Explanation of Benefits (EOB) from the primary payer. When a patient has coverage from more than one payer, Coordination of Benefits (COB) rules require the secondary payer to know how the primary payer adjudicated the claim before it can calculate its own payment. For Medicare Secondary Payer (MSP) claims, this requirement is especially strict — Medicare needs to see what the primary insurer paid or denied before it will process the secondary portion.
The primary EOB contains critical information the secondary payer needs: the billed amount, the allowed amount, what the primary payer paid, what was applied to the patient's deductible and coinsurance, and what was denied or not covered. Without this data, the secondary payer cannot determine its share of the remaining balance and will deny the claim.
N479 often occurs when the automatic crossover process between payers fails or does not exist. Many payers have electronic crossover agreements where the primary payer automatically forwards claims data to the secondary payer, but when this automation breaks down — or when no crossover agreement exists — the provider must manually submit the primary EOB with the secondary claim.
What to Do
Obtain the primary payer's EOB or electronic remittance advice for the claim. If you have not received the primary remittance yet, follow up with the primary payer to get it. Once you have the primary EOB, attach it to the secondary claim — for electronic claims, populate the COB loop in the 837 transaction with the primary payer's adjudication data; for paper claims, include a copy of the primary EOB with the resubmission.
Resubmit the claim to the secondary payer with complete primary payment information. If the automatic crossover process should have forwarded this data, report the crossover failure to both the primary and secondary payers so they can investigate and prevent it from affecting other claims. For practices that routinely bill secondary payers, building a workflow that holds secondary claim submission until primary adjudication is confirmed and COB data is available can prevent N479 denials.
Common Scenarios
- A patient has employer-sponsored insurance as primary and Medicare as secondary, but the provider submits to Medicare without attaching the primary insurer's EOB
- The electronic crossover between a primary commercial payer and Medicaid (secondary) fails for a batch of claims, and each one is denied with N479
- A billing specialist submits a secondary claim before the primary payer has finished processing, so no EOB exists yet to attach to the claim
Commonly Paired With
RARC N479 commonly appears alongside these CARC denial codes: