Determination of the primary insurer for members is based on the laws governing Medicare as a secondary payer, in which the plan assumes the position of Medicare in the order of benefit determination. When a member also has coverage through an employer group plan, the following rules may apply.

When the subscriber is an active employee or spouse of an active employee age 65 or older, and is covered by an employer group insurance plan and a Medicare plan:

When a member age 65 or older is an active employee (or spouse) of an employer with 20 or more employees and refuses to accept the health coverage offered by the employer, the plan must pay as primary. The plan may not assert that the active employee be covered by the employer group health plan when the member has decided not to participate in the employer group plan.

In determining the order of payers, the law specifies the threshold of number of employees to be 20 or more. Contact the Medicare Provider Services Department for assistance in determining the number of people employed by an employer-sponsor of the member's health plan.

When a member age 65 or older is a retiree or a spouse of a retiree, the plan is primary.

When an actively employed group member under age 65 (most often a spouse or child) is disabled and does not have end-stage renal disease (ESRD), and total disability is the sole basis for Medicare coverage, and has an employer group plan and a plan:

In determining the order of payers, the law specifies that a group is affected when the employer normally employs at least 100 employees on a typical business day during the previous calendar year. Contact the Medicare Provider Services Department for assistance in determining the number employed by an employer-sponsor of the member's health plan.

When an employer group member (most often a spouse or child) belongs to either an active or retiree plan through an employer group plan and ESRD is the sole basis for Medicare coverage (for example, the member is not age 65 or over or totally disabled), the employer group plan is primary for the first 30 months of Medicare eligibility. This rule applies regardless of whether the group coverage is provided through active employment or retirement, and regardless of the number of employees of the employer who sponsors the group plan. Original Medicare or the Medicare Replacement plan is primary after the first 30 months of Medicare eligibility.

Only the Medicare contractor for the participating provider's geographic area can determine the date on which Medicare becomes primary for ESRD Medicare beneficiaries. For each case, contact the Medicare contractor to determine the date that Medicare is primary.