Final answer:
Medicare is generally billed first for a 66-year-old woman with dual coverage under Medicare and her husband's private insurance, as Medicare is the primary payer. Coordination of benefits rules apply to ensure accurate billing and payment distribution.
Step-by-step explanation:
When billing for a 66-year-old woman who has Medicare and is also covered under her husband's private insurance, Medicare is generally billed first. This is because Medicare is a federal health insurance program that provides coverage to individuals who are 65 and older, regardless of income, medical history, or health status.
As established in 1965, Medicare is a primary payer for those eligible, and other private insurance plans are typically considered secondary payers. In the case where the individual has both Medicare and another form of private insurance (such as a spouse's employer-based insurance), the billing process usually follows the coordination of benefits rules which determine that Medicare is billed before the private insurance.
This coordination ensures that the billing is done correctly and that the insurance providers pay their appropriate share of the covered services. Therefore, the answer to the question regarding which entity is billed first would be B-Medicare.