How FHIR APIs Work

Beth Plumptre
October 18, 2023

In modern care delivery, interoperability is at the core of care operations, which is why information systems are now designed to push seamless data exchange through innovations like Fast Healthcare Interoperability Resources (FHIR) APIs.

FHIR APIs represent standardization, scalability, and flexibility — important features when optimizing for large-scale healthcare information exchange.

In this guide, we'll explore how the FHIR standard is changing the landscape of healthcare IT, from electronic health records (EHRs) and health information exchange (HIEs), to healthcare applications and other data-sharing systems.

What is FHIR?

FHIR is a standardized healthcare data exchange framework developed by Health Level Seven International (HL7). Before these resources were created, health data systems were in a uniquely challenging position.

When information sharing wasn’t done primarily via clunky methods such as fax and physical mail transfer, the exchange structures in place like HL7 V2, Clinical Document Architecture (HL7 CDA), and Consolidated CDA (C-CDA) were largely complex. These structures required extensive customization to support exchange between different healthcare organizations, and their multiple versions often led to compatibility issues between different systems.

FHIR was designed to address challenges associated with sharing healthcare data across different systems, despite diverse data formats and protocols. It leverages modern, open-web technologies to facilitate data exchange so retrieving patient medical history can be as simple as browsing the internet.

At its core, HL7 FHIR is based on a set of resources, each representing a specific piece of clinical or administrative data — such as patient records, medications, allergies, and lab results, for example. These resources introduce structure into data organization, while simplifying the process of querying, accessing, and retrieving patient data from electronic health records and other databases. 

Understanding FHIR APIs

An Application Programming Interface (API) is a bridge or entry point through which one computer program can access the data and features of another system. This interface ensures that computer systems can communicate with each other to easily share and exchange data.

Flowing from this, FHIR APIs stick to the FHIR standard, allowing healthcare systems, applications, and developers to exchange HL7 messages in a standardized format. FHIR APIs simplify data exchange between EHRs, HIEs, health applications, and other systems through core features that enable seamless transfers.

These key components include:


FHIR resources are the building blocks of the framework, representing a concept related to healthcare. Here, each block contains valuable information structured in a way that encourages easy data exchange.

Example FHIR resources include: "Encounter", "MedicationRequest", and "Observation".

Resources are designed to be machine and human readable.


FHIR APIs predominantly use HTTP (Hypertext Transfer Protocol) as the communication protocol. These resources are specific URLs or web addresses that carry out the behind-the-scenes work for accessing and retrieving clinical documents.

This means that data is exchanged using open web technologies via standard HTTP methods like GET, POST, PUT, and DELETE. HTTP resources are also useful for updating and deleting necessary data. An example of this can be found in the Metriport API docs.

RESTful Architecture

FHIR follows a RESTful approach when designing its APIs and data exchange structures. This means FHIR APIs are resource-based with a unique URL identifier, just like a web page.

Source: Codecademy

Likewise, RESTful APIs have simpler mechanisms of actions, as each request from a client — say, a healthcare application or EHR — is treated as new. This way, servers do not waste valuable memory storing past interactions, only the information needed to process a specific request is necessary for data retrieval.

How FHIR APIs Work

When a provider requires a patient’s information to continue care, he’ll typically request these records from an EHR, Mobile health app, or other health data system. This application then sends an HTTP request to a FHIR API, which as mentioned usually includes a specific URL listing the resource to be accessed, or other filtered record.

As a secure platform; this data request is usually first authenticated with the FHIR server to ensure only authorized personnel can request and access the data to be retrieved.

Once authenticated and authorized, the FHIR API works its way into the receiver’s system database, where it retrieves the necessary information. The data collected then undergoes FHIR conversion, so it is formatted according to the health data standards required before the information is returned to the client.

This data is then accessible and displayed to healthcare providers and other relevant players.

Benefits of FHIR APIs

FHIR APIs have whipped the healthcare landscape into a lean, efficient, data sharing machine.

These systems have not only minimized the need for manual data entries and paperwork, but have shaved the time typically spent maneuvering these challenges, permitting healthcare providers more time to focus on patient care.

Likewise, in addition to putting the patient at the center of their welfare, FHIR APIs are also innovation drivers in healthcare. FHIR implementation encourages developers to build on existing applications and services that leverage data, simplifying the learning curve to improve medical data infrastructure. 

By following FHIR specifications, these experts can boost different types of care delivery services from telemedicine to remote monitoring, and personalized medicine.

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