US Core Implementation Guide
5.0.1 - STU5 Release United States of America flag

US Core Implementation Guide, published by HL7 International - Cross-Group Projects. This is not an authorized publication; it is the continuous build for version 5.0.1). This version is based on the current content of https://github.com/HL7/US-Core/ and changes regularly. See the Directory of published versions

General Guidance

Referencing US Core Profiles

The search expectations and US Core Profiles have been developed and tested using logical FHIR ids. Therefore a reference to a US Core resource should include a logical id (Reference.reference), not an identifier (Reference.identifier).

Many of the profiles in this guide reference other FHIR resources that are also US Core Profiles. This is defined in the formal profile definitions. For example, US Core CareTeam Profile references US Core Patient. For any other references to base FHIR resources1 or not formally defined in a US Core Profiles, the referenced resource should be a US Core Profile if a US Core Profile exists for the resource type. For example, although Condition.asserter is not constrained by this guide, the reference to Patient or Practitioner should be a valid US Core Patient or US Core Practitioner. US Core Resources in the differential view and marked as “Must Support” follow the Must Support rules. Other resources allowed in the base FHIR specification may be referenced. For example, RelatedPerson is an allowed target reference in DocumentReference.author.

Contained Resources

When responding to a query, servers should not use inline contained resources to represent the returned data. The only time contained resource can be used is when the source data exists only within the context of the FHIR transaction. For example, the guidance in the Medication List page describes how a contained Medication in MedicationRequest is used for representing the medication. If referencing a contained resource in a US Core Profile, the contained resource should be a US Core Profile if a US Core Profile exists for the resource type. Further guidance about the general use case for contained can be found in the base FHIR specification.

Suppressed Data

In situations where the specific piece of data is hidden due to a security or privacy reason, using a code from the DataAbsentReason Code System such as masked may exceed the data receiver’s access rights to know and should be avoided. For elements with a minimum cardinality = 0 (including elements labeled Must Support), the element should be omitted from the resource. For Mandatory elements (in other words, where the minimum cardinality is > 0), use the code unknown following the guidance on Missing Data in the Conformance Sections.

Using UCUM codes in the Quantity datatype

Both the US Core Vital Signs Profile and US Core Laboratory Result Observation Profile bind the valueQuantity datatypes to the UCUM code system. A FHIR UCUM Codes value set that defines all UCUM codes is in the FHIR specification. This guidance specifies how to represent the Quantity datatype when the correct UCUM units are missing or the units are missing altogether which will likely occur in the real world.

UCUM code provided

 "valueQuantity": {
    "value": 26.0,
    "unit": "g/mL",
   "system": "http://unitsofmeasure.org",
   "code": "g/mL"
  }

free text units only:

  • If UCUM units are not available then represent units in the unit element.
 "valueQuantity": {
    "value": 26.0,
    "unit": "RR",
     }

no units

 "valueQuantity": {
    "value": 26.0
 }

Representing Entered in Error Information

Clinical information that has been entered-in-error in the patient’s record needs to be represented by the FHIR Server in a way so that Clients can expose the corrected information to their end users.

Server Recommendations:

  • A FHIR Server should not delete resources.
  • A FHIR server should update the appropriate resource status to entered-in-error or inactive.
  • A FHIR Server should allow these resources to be searchable by client applications.
  • If the FHIR server has updated the resource status to entered-in-error:
    • For patient facing applications, A FHIR Server should remove the contents of resource leaving only an id and status. Note this typically will not be conformant with the US Core or FHIR StructureDefinitions.
    • For provider facing applications, the content may be supplied with content and additional detail (such as the reason for the status change) that the patient viewing system would typically not have access to.

Representing Deleted Information

A FHIR Server should not delete records. If a system supports deletion of records, they should refer to the Deletion Safety Checks in the FHIR specification.

Narrative

The US Core CarePlan Profile requires a narrative summary of the patient assessment and plan of treatment. However, any US Core Profile may include a human-readable narrative that contains a summary of the resource and may be used to represent the content of the resource to a human. For further guidance, refer the Narrative documentation in the FHIR Specification.

Language Support

There is a basic need be able to access records in your language, and the data provider should do their best to translate (safely) to the language being requested. Understanding that this will be variably complete depending on the nature of the record. For example translating the following elements is relatively straightforward:

  • Coding.display
  • Generated narrative
  • Attachment.title

The following guidelines outline how to request and return a resource in the requested language.

  • Clients MAY request language/locale using the http Accept-Language header.
  • Servers should make reasonable efforts to translate what can be safely translated.
  • Servers should populate the Resource’s language element with a code which is based on the underlying language of record, not the requested language.
    • Using the http://hl7.org/fhir/StructureDefinition/language extension when the language of a display, etc is known to be different to the stated (or inferred) language.

      Example

          <?xml version="1.0" encoding="UTF-8"?>
          <Patient xmlns="http://hl7.org/fhir">
              <id value="language-example-1"/>
              <meta>
              [...snip...]
              </meta>
              <language value="es"/>
              <!--0..1 Language of the resource content in this case Spanish-->
              <text>
              [...snip...]
              </text>
              <extension url="http://hl7.org/fhir/us/core/StructureDefinition/us-core-race">
                  <extension url="ombCategory">
                      <valueCoding>
                          <system value="urn:oid:2.16.840.1.113883.6.238"/>
                          <code value="2106-3"/>
                          <display value="White">
                              <!--Human Language extension-->
                              <extension url="http://hl7.org/fhir/StructureDefinition/language">
                                  <valueCode value="en"/>
                                  <!--English is different from stated language-->
                              </extension>
                          </display>
                      </valueCoding>
                  </extension>
              [...snip...]
      
  • Using the http://hl7.org/fhir/StructureDefinition/translation extension when the server is providing additional translations by its own choice or in response to a different Accept-Language than what the resource is stored in.

    Example

          <?xml version="1.0" encoding="UTF-8"?>
          <Patient xmlns="http://hl7.org/fhir">
              <id value="language-example-2"/>
              <meta>
              [...snip...]
              </meta>
              <language value="en"/>
              <!--0..1 Language of the resource content: English-->
              <text>
              [...snip...]
              </text>
              <extension url="http://hl7.org/fhir/us/core/StructureDefinition/us-core-race">
                  <extension url="ombCategory">
                      <valueCoding>
                          <system value="urn:oid:2.16.840.1.113883.6.238"/>
                          <code value="2106-3"/>
                          <display value="White">
                          <!-- Translation -->
                          <extension
                               url="http://hl7.org/fhir/StructureDefinition/translation" >
                           <extension url="lang"> <!-- 1..1 Code for Language -->
                            <valueCode value="es"/><!-- 0..1 Value of extension -->
                           </extension>
                           <extension url="content"> <!-- 1..1 Content in other Language -->
                            <valueString value="Blanca">
                           </extension>
                          </extension>
                          </display>
                      </valueCoding>
                  </extension>
                  [...snip...]
    
  • Servers should make it known what languages are supported in their CapabilityStatement(s) using this extension2:

    http://hl7.org/fhir/5.0/StructureDefinition/extension-CapablilityStatement.acceptLanguage

For further guidance on language and locale for generation of the resource narrative, see the Multi-language support for Narratives in the core specification.

Read (Fetch) Syntax

For fetching a resource interactions on profile pages are defined with the following syntax:

GET [base]/[Resource-type]/[id] {parameters}

  • GET is the HTTP verb used for fetching a resource
  • Content surrounded by [] is mandatory for the client to supply, and will be replaced by the string literal identified.
  • Content surrounded by {} is optional for the client to supply, and will be replaced by the string literal identified.
    • parameters: URL parameters as defined for the particular interaction (e.g.”?_format=xml”}

For more information see the FHIR RESTful API

Search Syntax

The [FHIR RESTful Search API Requirements] Section define the rules for servers and clients that support the RESTful interactions defined in this guide.

All the search interactions in this guide use the GET command with the following syntax:

GET [base]/[Resource-type]?[parameter1]{:m1|m2|...}={c1|c2|...}[value1{,value2,...}]{&[parameter2]{:m1|m2|...}={c1|c2|...}[value1{,value2,...}]&...}

  • GET is the HTTP verb used for fetching a resource
  • Variables surrounded by “[]” are mandatory for the client to supply, and will be replaced by the string literal identified.
  • Variables surrounded by “{}” are optional for the client to supply, and will be replaced by the string literal identified.
    • base: The Service Root URL (e.g. “https://fhir-open-api-dstu2.smarthealthit.org”)
    • Resource-type: The name of a resource type (e.g. “Patient”)
    • parameter: the search parameters as defined for the particular interaction (e.g.”?patient=Patient/123”)
    • value: the search parameter value for a particular search
      • When searching using the token type searchparameter (how to search by token), the syntax {system|}[code] means that the system value is optional for the client to supply.:
      • When searching using the reference type searchparameter (how to search by reference), the syntax {Type/}[id] means that the Type value is optional for the client to supply:
      • When searching using the date type searchparameter (how to search by date), the syntax data={gt|lt|ge|le}[date] means the date comparators “gt”, “lt”, “ge”, and “le” are optional. Date type searches without a comparator prefix are equivalent to searches with the “eq” comparator even if a server does not support the comparator.
    • {:m1 m2 …}: The list of supported search parameter modifiers
    • {c1 c2 …}: The list of supported search parameter comparators
    • {,value2,…}: Optional multiple ‘OR’ Values
    • {&parameter2={:m1 m2 …}={c1 c2 …}[value1{,value2,…}&…}: Optional multiple ‘AND’ search parameters

In the simplest case, a search is executed by performing a GET operation in the RESTful framework:

GET [base]/[Resource-type]?name=value&...

For this RESTful search, the parameters are a series of name=[value] pairs encoded in the URL. The search parameter names are defined for each resource. For example, the Observation resource the name “code” for search on the LOINC code. For more information see the FHIR RESTful Search API

Note that the patient may be implicit in the context in some implementations (e.g. using SMART). Then the patient parameter can be omitted:

GET [base]/[Resource-type]{?other-parameters}

Searching Multiple Patients

Currently, most EHRs permit queries that provide a single patient id, but do not support the comma separated query or a query where the patient parameter is omitted as described in the standard FHIR REST API. Instead, a user facing app can perform multiple “parallel” queries on a list of patient ids. Alternatively, the FHIR Bulk Data Access (Flat FHIR) specification can be used to perform a “back end” system level query to access a large volumes of information on a group of individuals or when trying to identify and query against an unknown population such as when looking for population based research data or for population-level queries for public health surveillance.

However, neither specification defines how a user facing provider app is able to seek realtime “operational” data on multiple patients (such as all patients with recent lab results). Opportunities to add this capability to this guide are discussed in Future of US Core

This IG does not support patient compartment based searches.

Across Platform Searches

US Core servers are not required to resolve full URLs that are external to their environment.

Limiting The Number Of Search Results

In order to manage the number of search results returned, the server may choose to return the results in a series of pages. The search result set contains the URLs that the client uses to request additional pages from the search set. For a simple RESTful search, the page links are contained in the returned bundle as links. See the managing returned resources in the FHIR specification for more information.


Footnotes:

  1. For example, the base Location resource is being referenced by the US Core Encounter and US Core PractitionerRole resources. 

  2. This extension is converted from a new element in a future version of CapabilityStatement.