Guide 01 — FHIR · API · MCP · RAG · LLM
Five terms. Five different jobs. A more connected healthcare.
A side-by-side terminology map of the five terms most often confused in healthcare AI conversations.
A4 sheet — scroll sideways or pinch to zoom
Visual Guide 01 · Technical / GenAI
FHIR · API · MCP · RAG · LLM
Five terms. Five different jobs. A more connected healthcare.
Healthcare AI Learning
| Term | FHIRHealthcare data standard | APISoftware interface | MCPAI integration protocol | RAGArchitecture pattern | LLMAI model |
|---|---|---|---|---|---|
| What is it? | HL7 standard for representing and exchanging healthcare data. | An interface that lets systems request data or perform actions. | Open protocol standardising how AI/LLM applications connect to external context, data sources and tools. | Retrieval-augmented generation: retrieve external information and supply it as model context. | Large language model trained to process and generate language, and often other content. |
| Main purpose | Structure and exchange health data consistently. | Communication between systems. | A consistent AI-facing integration layer. | Provide relevant, current or private information at runtime. | Understand, reason over and generate output from prompt and context. |
| Key capabilities | Standardised resource models (Patient, Observation, Condition); several exchange paradigms — REST, documents, messaging. | Request/response, authentication and authorisation, structured exchange. | MCP servers can expose resources, prompts and executable tools. | Search, retrieve, rank and supply relevant content. Vector search is one possible mechanism, not the definition. | Summarise, classify, transform and generate content, depending on model and input. |
| Healthcare example | Patient + Observation (HbA1c) + Condition records. | A FHIR API endpoint retrieving the latest lab results. | An MCP server exposing a “get patient observations” tool that internally calls an approved API/FHIR service. | Retrieve a current guideline plus relevant patient context before a model drafts a response. | Draft a concise clinical summary from supplied context. |
| Often confused with | An API, or a database. | A data standard, or an AI model. | A replacement for APIs or FHIR. | A model, a database, or a training method. | A source of truth, or a database. |
| What it is NOT | Not an AI model, and not limited to REST APIs. | Not a data standard, and not a data source on its own. | Not an EHR, not a healthcare data standard, not a model. | Not a model, not the same as a vector database, and no guarantee of correctness. | Not automatically connected to hospital data; it does not know private or current organisational data unless that is provided through context, retrieval, tools or another integration. |
How they work together in practice
Healthcare data sources
EHR, lab, imaging, devices, notes
Interoperability layer
FHIR, APIs, SMART on FHIR, DICOM, terminologies
Access & retrieval
RAG, MCP, direct API, context assembly
AI application
LLM, agent, tools, guardrails, evaluation
Output & impact
Reviewed output used in the workflow
Paths overlap. An MCP tool can call an API — including a FHIR API — and RAG can retrieve through APIs.
Common misconceptions
- “FHIR is an API.” Not quite. FHIR is a healthcare data standard and exchange framework; REST APIs are one major way to use it.
- “MCP replaces APIs.” No. MCP standardises the AI-facing integration layer and may call existing APIs underneath.
- “RAG is a database.” No. It is a retrieval-plus-generation pattern; a vector database is one possible retrieval component.
- “An LLM knows our hospital data.” Not unless that data is supplied or connected through context, retrieval or tools.
- “If we have FHIR, our data is AI-ready.” No. Relevance, timing, provenance, coding consistency, missingness and task fit all still matter.
FHIR R5 (5.0.0) is the current published core FHIR release. · Many real deployments still run R4/R4B. · SMART App Launch 2.2 is based on FHIR R4. · Always inspect the actual server CapabilityStatement and implementation guide.
Related learning
Guides summarise the same primary sources cited in the related courses — official EU legal texts, standards bodies and peer-reviewed literature. Educational summaries only, not legal or clinical advice; regulatory dates were checked between 25 August and 10 September 2026.
Updated Sep 2026