MA18MA-series (Medicare alerts & claim-level)Alerts & Appeals
MA18: Alert: claim crossed over to supplemental insurer
Medicare automatically forwarded this claim to the patient's supplemental insurer — no separate secondary submission needed.
What to do about it
Don't rebill the secondary (you'll generate N522 duplicates). Post the Medicare payment and await the supplemental remit; follow up only if nothing arrives in ~30 days.
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