When you become eligible for End-Stage Renal Disease (ESRD) Medicare, your employer group health plan will pay first and Medicare will pay second. This is called the 30-month coordination period. The 30-month coordination period begins when you are first eligible for Medicare based on ESRD, even if you haven’t signed up for it yet. For example, if Mr. X begins dialysis at a facility in September of 2011, he is eligible for Medicare the first day of the fourth month he gets dialysis, which is December 1, 2011. Mr. X does not enroll in Medicare until June, 2012. His 30-month coordination period still began on December 1, 2011.
The 30-month coordination period applies to current employer insurance, retiree insurance and COBRA. They all pay first and Medicare pays second. After the 30-month coordination period, Medicare will pay first for all Medicare-covered services and your employer group health plan will pay second.
If you do not have any insurance but Medicare, Medicare pays primary on all claims as soon as you enroll.