Medicare Administrative Contractor (MAC)

CMS does not process Original Medicare claims itself. It hands that work to private insurers, each awarded a geographic jurisdiction. There are 12 A/B MACs for Part A and Part B claims and 4 DME MACs for durable medical equipment, prosthetics, orthotics and supplies, and four of the A/B MACs also process home health and hospice claims for areas that do not match their A/B territory¹.

For a practice, the MAC is Medicare in every practical sense. It enrolls you, processes and pays your claims, answers provider inquiries, teaches billing requirements, sets local coverage determinations, reviews medical records on selected claims and decides redetermination requests, the first level of appeal¹. That first appeal is handled by MAC staff who had no part in the original claim decision³.

For Part A and Part B claims, which MAC you bill depends on where you are, not where the patient lives. A/B providers are assigned to the MAC that CMS contracts for the area where the provider is physically located, while a DMEPOS supplier sends claims to the DME MAC for the area where the beneficiary permanently resides². A practice that opens a location in another MAC’s territory enrolls with that MAC as well⁴.

The mistake is treating one MAC’s guidance as national. Local coverage determinations are written by each MAC for its own jurisdiction, so a coverage rule copied from another region’s contractor website can be wrong for your claims. Read the policies, forms and portal instructions of the MAC that pays you.