Block 17a is used for which identifier?

• A. The National Provider Identifier (NPI) number.
• B. The practice's tax identification number.
• C. The physician's medical license number.
• D. The patient's insurance policy number.

Answer: (B)

Block 17a is used for the practice’s tax identification number. This identifier ties the claim to the billing entity for tax reporting and IRS purposes, ensuring payments are reported to the correct organization. The National Provider Identifier (NPI) is a separate identifier used to identify individual providers in transactions, and it appears in other parts of the form or in electronic claims. The physician’s medical license number isn’t used for billing on the CMS-1500, and the patient’s insurance policy number is for verifying coverage, not for identifying who is submitting the claim. Therefore, the tax identification number is the correct identifier for this block.