Learn FHIR R4
Plain-English answers to the most common questions about HL7 FHIR R4 — the healthcare interoperability standard. New to FHIR? Start here, then jump into the full resource reference.
What is FHIR?
FHIR (Fast Healthcare Interoperability Resources) is an open standard from HL7 for exchanging healthcare data over a web-style API. It defines a set of modular building blocks called resources — Patient, Observation, Medication, Encounter, and so on — that can be combined to represent any clinical or administrative concept. Each resource has a defined structure, a JSON or XML wire format, and a RESTful API for read, write, search, and history.
What is FHIR R4?
FHIR R4 (release 4, version 4.0.1, published in 2019) is the first version of FHIR with normative content — meaning the core resources and infrastructure are stable and backwards-compatibility is guaranteed. Most production healthcare systems today, including the US Core profile required by the ONC Cures Act and most national implementations, target FHIR R4.
What is the difference between FHIR and HL7 v2?
HL7 v2 is a 1980s pipe-delimited messaging standard still widely used inside hospitals for ADT, orders, and results. FHIR is a modern REST + JSON standard designed for web and mobile, with a richer data model, terminology bindings, and discoverable APIs. FHIR is meant to complement, not immediately replace, v2 — many systems bridge the two.
What is a FHIR resource?
A FHIR resource is a self-contained unit of healthcare data with a defined schema, identity (id), metadata (meta), and a set of typed elements. Resources are the basic units of exchange in the FHIR API: you read, write, and search resources by type. There are 145 resources in R4, grouped into Foundation, Base, Clinical, Financial, and Specialized categories.
What is the FHIR API?
The FHIR API is a RESTful HTTP interface for exchanging FHIR resources. The most common interactions are GET [base]/Patient/123 (read), GET [base]/Observation?subject=Patient/123 (search), POST [base]/Patient (create), PUT [base]/Patient/123 (update), and DELETE. Servers also support history, batch, and transaction bundles, plus operations ($everything, $validate, etc.) for things that don't fit pure REST.
What is a FHIR Patient resource?
The Patient resource holds demographic and other administrative information about an individual receiving healthcare services — name, gender, birth date, addresses, telecom contact points, identifiers, and links to other Patient or RelatedPerson records. It is the most commonly referenced resource in clinical FHIR and is required by virtually every implementation guide.
What are FHIR search parameters?
Search parameters define the queryable axes of each resource. For example, Patient supports name, family, given, birthdate, identifier, and gender. Each search parameter has a type (string, token, date, reference, quantity, uri, number, composite, special) and a FHIRPath expression that points at the element(s) it indexes. They can be combined, chained, and modified (e.g. :exact, :contains, :missing).
What is a FHIR value set?
A value set is a curated collection of coded concepts drawn from one or more code systems (LOINC, SNOMED CT, ICD-10, RxNorm, custom systems, etc.). Resource elements with a coded type carry a binding to a value set plus a binding strength (required, extensible, preferred, example) that tells implementers how strictly to enforce the codes.
What is a FHIR Bundle?
A Bundle is a container resource for a collection of other resources. It is used for search results (type: searchset), transactions and batches (type: transaction / batch), documents (type: document), messages (type: message), and history (type: history). Bundles are how FHIR sends more than one resource in a single HTTP response or request.
What is a FHIR profile?
A profile (StructureDefinition) constrains a base FHIR resource for a specific context — making elements required, fixing terminology bindings, narrowing cardinalities, or adding extensions. Profiles are how implementation guides like US Core, IPS, and country-specific guides specialize the generic R4 resources for real-world use.