By Lisa Nelson, Chief Technical Officer
When you think about interoperability, chances are you picture data exchange – clinical summaries, referrals, patient records moving from one system to another. But none of that works without knowing where to send the information and how to find the right recipient.
Between 2020 and 2024, the DirectTrust® Directory underwent a full-scale transformation of the Directory’s technical foundation, data quality practices, and policy framework. Now, the Directory isn’t just more robust – it’s more useful, more accurate, and better aligned with the real-world needs of interoperability today.
How the Directory Was Improved Using FHIR
The technical overhaul implemented over 60 new validation rules to improve the quality of submitted data, added support for incremental updates, and shifted focus from a single “white pages” mentality (listing individual clinicians) to a dual “white- and yellow-pages” model that includes departmental and workflow-specific Direct addresses. The expanded approach aligns better with how organizations process information and search for Direct addresses. Most importantly, the once flat structure of Directory’s data was transformed. Using standard FHIR resources with relationships between organizations, locations, and practitioners, endpoints (Direct addresses) can now be associated with the right parts of the structure – a structure which is more reflective of how healthcare actually works.
DirectTrust implemented a FHIR-based directory model based on multiple directory standardization efforts led through HL7. Over the past decade, three distinct directory standardization initiatives have iteratively improved FHIR directory specifications and produced consistent modeling patterns.
Initially, HL7’s Validated Healthcare Directory Implementation Guide introduced FHIR profiles for 10 key FHIR resources required to represent “healthcare entities.” This implementation guide uses the term ‘healthcare directory’ instead of ‘provider directory’ because its scope encompasses all entities that provide services impacting health and well-being. This was a key consideration for us because the DirectTrust Aggregated Directory covers both healthcare and socialcare organizations.
Foundational FHIR Resource Profiles established by the Validated Healthcare Directory IG
The Validated Healthcare Directory IG established the foundational structural relationships to represent healthcare directory information using FHIR. The structural patterns were reaffirmed and strengthened through two subsequent directory standardization efforts: Da Vinci PDex Plan Net and FAST National Directory of Healthcare Providers and Services (NDH).
Two Key Structural Patterns Establish the Shape of Directory Information
The understanding of two key relationship patters is critical to appreciating the value of this early directory modeling work, PractitionerRole and OrganizationAffiliation.
PractitionerRole: The FHIR PractitionerRole Resource describes the relationship between a practitioner and an organization. A practitioner provides care services in the context of working for an organization at a location. Practitioners also participate in healthcare provider insurance networks through their role at an organization, but this part of the pattern is not applicable to the DirectTrust Directory at this time.
OrganizationAffiliation: Similar to PractitionerRole, the FHIR OrganizationAffiliation Resource describes relationships between organizations. For example: 1) the relationship between an organization and an association it is a member of (e.g. hospitals in a hospital association), 2) an organization that provides services to another organization, such as an organization contracted to provide mental health care for another organization as part of a healthcare provider insurance network, and 3) distinct organizations forming a partnership to provide services (e.g. a cancer center).
The DirectTrust Aggregated Directory FHIR Model
The goal of the DirectTrust Aggregated Directory is to enable a single comprehensive, searchable collection of all available Direct addresses tied to their associated identity-verified entity. The Directory does not include provider insurance network participation information, nor does it offer detailed healthcare service offerings. Given this narrower focus, the DirectTrust Directory model only requires a subset of the established FHIR Resource Profiles:
The DirectTrust Aggregated Directory uses only the FHIR resources needed, but follows the established resource relationship patterns between organizations, locations, and practitioners so that endpoints (Direct addresses) are associated with the right parts of the structure to reflect how health and social care services are delivered today.
The FHIR Endpoint Resource
Further, thanks to the FHIR-based Directory model, the DirectTrust Aggregated Directory now supports more metadata per endpoint. New use case codes have been established to clarify what each Direct address is prepared to support (i.e., referrals, ADT notifications). This provides valuable context for Directory listings and makes the Directory a more powerful lookup resource.
The FHIR Endpoint Resource structure makes it possible to record more than just a Direct address. Fields like connectionType, payloadType, and payloadMimeType make it possible to include useful metadata that helps data sharing partners understand the type of interoperability supported by an Endpoint.
More Expressive Endpoint Information Is Required
The evolving body of interoperability experience has revealed that directories need to expose more detailed endpoint information to enable connectivity. The FAST NDH Implementation Guide includes a robust FHIR Endpoint Profile with numerous extensions designed to carry richer, more granular endpoint details needed to deliver on the promise of interoperability. The DirectTrust Directory is now positioned to leverage some of the established Endpoint extensions, such as Endpoint-usecase, to meet implementer needs for more information about what capabilities each endpoint can support.
Mature Directory Governance Is Essential
DirectTrust’s governance over the Directory plays a key role in enabling technology advances to yield positive outcomes. The Directory Policy Workgroup, made up of HISPs, vendors, providers, and technical experts, identified a set of policy drivers to help drive progress made possible by technical improvements. The changes introduced mandatory participation in the Directory for all HISPs and minimum participation levels for DSM adopters. They established tighter cycles for contributing and redistributing updated Directory listing content, permitted DirectTrust to introduce new public access Directory search tools enabled by the new FHIR APIs, and enabled greater cross-community collaboration.
These requirements and changes were made through policy updates and tied to HISP accreditation, which created a clear incentive for improvement. DirectTrust now boasts , better quality data, and a significant increase in Direct address awareness and overall usage of Direct Secure Messaging. This included a surge in the number of Direct addresses published in the Directory, which peaked at over 1.3 million before stabilizing at 1.2 million, and a 42% rise in message volume across the network in 2024.
What the Future Holds
DirectTrust is preparing for the next round of Directory improvements. As of mid-2025, we’re entering a new planning phase, which includes gathering input from across the ecosystem to identify emerging needs and ongoing challenges. The next cycle promises enhancements to the Directory search tool, new ways to keep Directory listings updated, and support for more useful Directory listings and more detailed endpoint descriptions.
This summer, at the DirectTrust Annual Conference in St. Louis, we’ll unveil the proposed plan for our next improvement cycle – gathered from months of listening, feedback, and hands-on collaboration. It’s a chance for attendees to weigh in, share needs and help guide what comes next.
Attend the DirectTrust 2025 Annual Conference to find out more about the roadmap forward!