NPI - yes, this is required.
Excerpt from August 2013 Medicaid Bulletin:
"Remember that all providers are to use taxonomy codes on all claims. Taxonomy codes identify the provider type and area of specialization for health care providers. They are 10-character alphanumeric codes that allow providers to identify their specialties. With the exception of pharmacy providers, all providers are required to submit taxonomy codes on all claims.
To learn more about NPI and find correct taxonomy codes visit www.ncdhhs.gov/dma/NPI/index.htm. Providers can see a full list of taxonomy codes from the Washington Publishing Company at www.wpc-edi.com/codes/taxonomy."
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