BlueCard program
When a patient carries a Blue Cross Blue Shield plan issued in another state, you don't file with their plan directly. Under BlueCard, you submit the claim to your local Blue plan (the host plan). It routes the claim electronically to the member's plan (the home plan), which processes it, and your local plan pays you under your contract with it (BCBS of Illinois: BlueCard; BlueCard Provider Manual).
The routing key is the three-character prefix at the start of the member ID. Report the ID exactly as it appears on the card, prefix included; a missing or wrong prefix is a common cause of rejections and delays.
For eligibility and benefits, the BlueCard eligibility line (1-800-676-BLUE) routes your call to the member's home plan by prefix. Your local plan remains your contact for claim status, payment problems and adjustments.
Medical policy still comes from the member's home plan, so a nutrition benefit can look different from what your local Blue members have.