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When Medicare is primary

If a Medicare member has secondary insurance coverage through one of our plans (such as the Federal Employee Program, Medex, a group policy, or coverage through a vendor), Medicare generally forwards claims to us for processing.

Once a month, Blue Cross forwards eligibility information (the member’s Medicare MBI number and effective dates of coverage) to the Centers for Medicare & Medicaid Services. Medicare uses this information when determining which claims should be forwarded to Blue Cross.

If: Then:
The Medicare MBI number is missing from our eligibility file
  • We will not send any member information to Medicare and claims will not automatically cross over to us from Medicare.
  • Ask the member to call our Coordination of Benefits Department at 1-800-839-8991 and give the representative their Medicare number.
  • Please bill us directly.
The Medicare MBI number we have on file is invalid
  • Claims for this member won’t cross over.
  • Ask the member to call our Coordination of Benefits Department at 1-800-839-8991 to revalidate the Medicare number.
  • Please bill us directly.
The member is an out-of-state federal employee
  • Send the secondary claims for out-of-state FEP members directly to us using your current billing process.


  • All paper claims must be accompanied by the corresponding Medicare explanation of benefits (EOB).
  • We must receive your paper claim within one year of the Medicare EOB’s processed date.
  • You must wait 30 calendar days after receiving the Medicare payment before submitting the secondary claim to Blue Cross. This is because it may take up to 30 calendar days after you receive Medicare’s payment for you to receive our payment or instructions. Medicare primary claims submitted to us within 30 calendar days of the Medicare payment date or with no Medicare payment date will be rejected.


 Coordinating with Medicare Fact Sheet

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