42 CFR §411.204

1. (a)Medicare benefits are secondary to benefits payable by an LGHP for services furnished during any month in which the individual—
   1. (1)Is entitled to Medicare Part A benefits under § 406.12 of this chapter;
   2. (2)Is covered under an LGHP; and
   3. (3)Has LGHP coverage by virtue of his or her own or a family member's current employment status.
2. (b)Individuals entitled to Medicare on the basis of disability who are also eligible for, or entitled to, Medicare on the basis of ESRD. If a disabled individual is, or could upon filing an application become, entitled to Medicare on the basis of ESRD, the coordination of benefits rules of subpart F of this part apply.