42 CFR §410.42

1. (a)General rule. Except as provided in paragraph (b) of this section, Medicare Part B does not pay for any item or service that is furnished to a hospital outpatient (as defined in § 410.2) during an encounter (as defined in § 410.2) by an entity other than the hospital unless the hospital has an arrangement (as defined in § 409.3 of this chapter) with that entity to furnish that particular service to its patients. As used in this paragraph, the term “hospital” includes a CAH.
2. (b)Exception. The limitations stated in paragraph (a) of this section do not apply to the following services:
   1. (1)Physician services that meet the requirements of § 415.102(a) of this chapter for payment on a fee schedule basis.
   2. (2)Physician assistant services, as defined in section 1861(s)(2)(K)(i) of the Act.
   3. (3)Nurse practitioner and clinical nurse specialist services, as defined in section 1861(s)(2)(K)(ii) of the Act.
   4. (4)Certified nurse mid-wife services, as defined in section 1861(gg) of the Act.
   5. (5)Qualified psychologist services, as defined in section 1861(ii) of the Act.
   6. (6)Services of an anesthetist, as defined in § 410.69.
   7. (7)Services furnished to SNF residents as defined in § 411.15(p) of this chapter.