An API, or application programming interface, is a set of tools that lets different healthcare software systems talk to each other and share data automatically. Think of it as a translator sitting between two programs that otherwise wouldn’t understand each other. When your doctor’s scheduling tool checks the electronic health record for open appointment slots, books your visit, and updates both calendars instantly, that’s an API at work. These connections power nearly every digital interaction in modern healthcare, from patient portals to billing systems to wearable fitness trackers feeding data to your clinician.
How Healthcare APIs Work in Practice
At the simplest level, an API is a request-and-response system. One piece of software asks a question, and another piece of software answers it, all without a human copying data between screens. A scheduling tool asks the electronic health record (EHR), “What slots are open Thursday?” The EHR responds with the available times. The scheduling tool confirms your booking and updates both systems at once.
That same pattern repeats across hundreds of healthcare workflows. A pharmacy system requests your prescription details from your doctor’s EHR. A billing platform pulls diagnosis codes to generate a claim. A patient portal retrieves your lab results so you can view them on your phone. Each of these exchanges follows the same basic logic: request, authenticate, deliver, confirm.
FHIR: The Common Language
For APIs to work across different hospital systems, software vendors, and apps, everyone needs to agree on a shared format. That standard is called FHIR (Fast Healthcare Interoperability Resources), developed by the standards organization Health Level 7. FHIR defines modular building blocks called “Resources,” each representing a specific piece of a patient record, like a medication, a lab result, or an allergy. These Resources specify exactly what data elements are included, how they relate to each other, and how they’re structured for exchange.
FHIR is built on the same web standards that power everyday internet applications, which makes it far easier for developers to work with than older healthcare data formats. Before FHIR, many systems relied on proprietary or closed communication methods, meaning a hospital using one EHR vendor often couldn’t easily share data with a clinic using a different one. FHIR doesn’t eliminate that problem entirely, but it gives everyone a common starting point. The federal government has made FHIR adoption a central requirement for certified health IT, and EHR vendors must now publish publicly accessible directories of their FHIR-compatible systems.
Why Healthcare Moved to REST Architecture
Most modern healthcare APIs use an architectural style called REST (Representational State Transfer), which replaced an older protocol called SOAP. The differences matter because they directly affect speed, flexibility, and cost.
SOAP APIs require XML formatting exclusively, produce larger and more complex messages, and force the server to remember the state of every previous interaction with a client. That makes them slower and harder to scale. REST APIs support multiple data formats (including the lightweight JSON format that FHIR uses), process each request independently, and produce smaller messages that transmit faster. REST also supports encryption natively without the performance penalty that SOAP’s additional security layer introduces. For modern applications like mobile health apps and cloud-based platforms, REST’s flexibility and speed make it the clear fit. SOAP still appears in some legacy hospital systems, but the industry trajectory is firmly toward RESTful architecture.
Security and Patient Privacy
Every API transaction involving patient data must comply with HIPAA, which means encryption, identity verification, and strict access controls are built into the design. Data moving through an API is encrypted using Transport Layer Security (TLS) version 1.2 or higher, the same type of encryption that protects online banking.
Authentication, the process of proving you are who you claim to be, typically relies on two layered protocols. OAuth 2.0 controls what data a third-party app is allowed to access and for how long, preventing unauthorized applications from pulling information they shouldn’t have. OpenID Connect sits on top of OAuth and verifies the identity of the person requesting access. Together, they allow you to log in to a patient portal, grant a health app permission to view specific records, and revoke that permission later, all without ever sharing your login credentials directly with the app.
Multi-factor authentication (requiring more than just a password) is recommended for patient portal access. Systems are also expected to support individual privacy preferences, so you can limit what types of data an app can see rather than granting all-or-nothing access.
Wearables and Remote Monitoring
APIs are the mechanism that moves data from your wrist to your doctor’s screen. Wearable devices like fitness trackers and smartwatches collect health data passively through sensors, then use APIs to send that data to aggregation platforms like Apple HealthKit or Google Fit. These platforms pool information from multiple health apps into one place.
Some devices can already connect directly to EHRs through these aggregators, transmitting simple data types like step counts, weight, and heart rate. But this integration is still evolving. Health systems often lack the infrastructure to ingest continuous streams of data from many different patient devices, and many device manufacturers still use proprietary communication methods. Third-party interoperability platforms have emerged to bridge these gaps, translating data from various wearable formats into something an EHR can understand and display.
How Widely APIs Are Used Today
API adoption in U.S. hospitals has grown rapidly. In 2024, 87% of hospitals reported that their patients could access health information through API-driven apps, up from just 39% in 2017. On the patient side, 65% of individuals accessed their online medical records or patient portal in 2024, more than double the 25% who did so in 2014. App-based access specifically has climbed from 38% in 2020 to 57% in 2024, a trajectory that accelerated after federal rules under the 21st Century Cures Act took effect.
Caregiver access has also expanded. The share of people accessing a patient portal on behalf of someone they care for jumped from 24% in 2020 to 51% in 2024. Portal-organizing apps that combine records from multiple providers (like Apple Health Records) are still niche, used by about 7% of individuals, but that’s up from 2% just two years earlier. Patients whose doctors actively encouraged them to use their portal accessed it at much higher rates: 87% compared to 57% among those who weren’t encouraged.
Barriers That Remain
Universal interoperability is still a work in progress. The data elements available through APIs vary by EHR vendor, which means developers sometimes need proprietary workarounds on top of the standardized FHIR interface. Many providers haven’t yet established FHIR-compatible endpoints, particularly smaller practices and public health agencies that lack the IT infrastructure and budget to implement them.
Financial incentives for data sharing remain unclear in many contexts. For patient-facing apps, sustainable business models are still developing. And trust between stakeholders, including hospitals, app developers, and patients, continues to be a friction point. Hospitals may be cautious about opening data access to third-party apps they don’t control, while patients may hesitate to grant permissions without fully understanding what data will be shared and how it will be used. Federal certification requirements are pushing the ecosystem toward openness, including mandates that EHR vendors verify and register third-party apps within 10 and 5 business days respectively, but the practical landscape is still catching up to the regulatory vision.