Which block is designated for writing the Coordination of Benefits Agreement Medigap-based identifier?

• A. Block 9a
• B. Block 9c
• C. Block 11b
• D. Block 10b

Answer: (B)

Coordination of benefits information for a Medigap plan is captured in the area of the CMS-1500 form that holds data about another insured. Within that section, there are separate spaces for different types of identifiers. The specific space reserved for a Medigap COB identifier is the subfield designated for Coordination of Benefits. Entering the Medigap-based identifier here keeps it linked to the secondary coverage and allows payer systems to properly coordinate benefits with Medicare. Other data in that same area, such as the primary policy number or other insured details, belong in their own subfields, so using the coordination-of-benefits subfield avoids mixing different identifiers and supports accurate processing.