Attach clinical documentation to a claim using the X12 275 additional information transaction linked via PWK segment

Verified steps

1. Note the May 2026 CMS final rule that adopted X12 version 006020 of the 275 and 277 implementation guides as the first HIPAA-mandated standards for health care claims attachments; verify whether your payer is operating under the new standard or a transitional arrangement.
2. In the originating 837 claim, populate the PWK segment at the appropriate loop level (claim or service line): PWK01 is the attachment report type code (e.g., OZ for support data for claim), PWK02 is the transmission method code (EL for electronic), and PWK06 is your unique attachment control number — format and uniqueness rules are payer-specific.
3. Construct the 275 transaction linking to the claim via the TRN segment: TRN01=1 (current transaction), TRN02 must match PWK06 exactly; include NM1 loops for submitter and receiver and the CAT segment to identify the document category.
4. Encode the clinical document in the BIN or BASE64 segment of the 275 depending on the payer's companion guide requirements; the total 275 transaction size is limited to 30 MB — split large records into multiple 275 transactions if needed.
5. Submit the 275 before or concurrently with the 837; some payers require the 275 to arrive before the claim is adjudicated — confirm timing requirements in the payer's companion guide.
6. Monitor for a 277 attachment acknowledgment; a 277 with a status code indicating the attachment was not linked to a claim means the PWK06/TRN02 matching failed — resubmit with corrected control numbers.