HCFA-1500 Box 33b - Other ID

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September 01, 2025

On the HCFA-1500 form, Box 33b is used to report the Billing Provider Secondary (legacy) Identification when required by the payer. This field complements Box 33a (NPI). Only populate Box 33b if the payer explicitly requests a non-NPI identifier for the billing provider.

Tip: Most payers only require the billing provider’s NPI in Box 33a. Enter a legacy ID in Box 33b only if specified by the payer. The correct qualifier must be used, followed by the assigned identifier.

In our example below, the billing provider reported qualifier 1G with ID 54321.

HCFA-1500 Box 33b - Billing Provider Secondary ID

In the X12 837P 5010 transaction, Box 33b maps to the 2010AA Billing Provider Loop in the REF segment:

  • REF01 – Reference Identification Qualifier
  • REF02 – Billing Provider Secondary Identification Number

Valid REF01 Qualifiers for Box 33b

  • 0B – State License Number
  • 1G – Provider UPIN Number

Sample 837P (5010) – Box 33b Mapping

> Billing Provider (2010AA) REF*1G*54321~

Additional Data

  • 2000A PRV03 – Taxonomy Code may also be reported for the billing provider to indicate provider specialty.

Note: Use Box 33b only when required by the payer. The qualifier must be either 0B (State License Number) or 1G (Provider UPIN Number). Most claims today only require the NPI in Box 33a, with Box 33b left blank unless otherwise directed.

For additional information on the X12 837 standard, please refer to the official implementation guides published by X12.

HCFA-1500 Form Box Locations

Grab a sample of the HCFA-1500 claim form here - HCFA 02/12 Claim Form


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