The billing entity's NPI should be reported in the 2010AA Billing Provider Loop of the 837P electronic claim or Item 33a of the CMS-1500 paper claim form. 

Important note: The NPI of the billing provider is required on all claims. Paper claims will be rejected as unprocessable and electronic claims may be rejected if:

• Any information appears to be missing or invalid in the 837P 2010AA loop, REF02. Item 33b of the paper form should be left blank.
• The billing provider's NPI is missing, invalid, or is in the wrong area (e.g., valid NPI submitted in Item 33b.)

Reminder: When billing services rendered by an individual associated with an incorporated entity or a group, the individual practitioner's NPI must be reported in the Rendering Physician's area (the 2310B Rendering Provider Loop of the 837P electronic claim or Item 24J of the paper claim form) and the billing entity or group identifier would be reported as indicated above. If you are an independent lab, ambulatory surgical center (ASC), independent diagnostic testing facility (IDTF), ambulance supplier, or solo practitioner not associated with a group, a rendering provider identifier in Item 24J or loop 2310B is not required when billing services.

 

Reference

CMS IOM Pub. 100-04 Medicare Claims Processing Manual, chapter 26 section 10.4