The Patient Identifier Cross-Referencing HL7 v3 (PIXV3) Integration Profile is part if the IHE IT Infrastructure technical framework.

This profile has the same functionality as the Patient Identifier Cross-referencing (PIX) Integration Profile. The differences in the new PIXV3 profile are in the format of the messages, and in the use of SOAP-based web services. These changes make this new profile well suited for use within an  existing IT infrastructure for cross-enterprise data access and exchange. This new profile supports the cross-referencing of patient identifiers from multiple Patient Identifier Domains. These cross-referenced patient identifiers can then be used by "identity consumer" systems to correlate information about a single patient from sources that "know" the patient by different identifiers. This allows a clinician to have a more complete view of the patient information.

Source: IHE IT Infrastructure Technical Framework Supplement 2008-2009: PIXV3 and PDQV3