This is from the Medicare Learning Network:
Relationship of the NPI to the PTAN
The NPI and the PTAN are related to each other for Medicare purposes. A provider must have one
NPI and will have one, or more, PTAN(s) related to it in the Medicare system, representing the
provider’s enrollment. If the provider has relationships with one or more medical groups or practices or with multiple Medicare contractors, separate PTANS are generally assigned.
Together, the NPI and PTAN identify the provider, or supplier in the Medicare program. CMS
maintains both the NPI and PTAN in the Provider Enrollment Chain & Ownership System (PECOS),
the master provider and supplier enrollment system.