Written by Technical Team | Last updated 25.10.2025 | 11 minute read
Understanding interoperability in digital health has become critical as health and care systems move towards data-driven models of prevention, diagnosis, treatment, reimbursement, and population health management. Interoperability is the ability of different systems, applications, devices, or organisations to exchange and make use of information. Within that, two concepts sit at the heart of safe, meaningful health information exchange: syntactic interoperability and semantic interoperability.
Although they are often discussed together, they solve very different problems. Confusing the two, or prioritising one at the expense of the other, can lead to systems that technically “talk” but fail to understand each other in a clinically trustworthy way. This article explores the differences between semantic and syntactic interoperability in digital health, why both matter, how they are implemented, and what challenges health systems face in trying to achieve them.
Syntactic interoperability refers to the ability of two or more health information systems to exchange data using a common format and structure. In other words, it ensures that data can physically move from System A to System B in a predictable, machine-readable way. It is concerned with the grammar of data exchange: message formats, file structures, APIs, and transport protocols. If syntactic interoperability is in place, messages do not break on arrival; they can be parsed, stored, and routed consistently across systems.
In health and care, syntactic interoperability is typically enabled by agreed technical standards that define how data should be packaged and transported. Widely used examples include HL7 V2 messaging, HL7 FHIR resources, DICOM for medical imaging, EDIFACT for administrative transactions, and CDA for clinical documents. These standards define rules such as field length, field order, optional versus required segments, data types, and expected structures of requests and responses. For instance, an HL7 admission/discharge/transfer message can be sent from a hospital’s patient administration system to a community record system, and both will recognise where to find the patient identifier, ward, consultant, and discharge status because the message follows a known schema.
Application programming interfaces (APIs) are another major enabler of syntactic interoperability. In modern health platforms, FHIR-based RESTful APIs, for example, expose specific “resources” such as Patient, Observation or MedicationRequest. When a system queries for a Patient resource, it gets back a JSON or XML bundle with clearly defined fields like name, NHS number or date of birth that any conformant consumer can parse. In this sense, syntactic interoperability is about creating a reliable pipe with well-labelled boxes travelling through it. The receiving system might not fully grasp the clinical nuance of what is inside each box, but at least it knows how to open and read it.
It is important to note that syntactic interoperability on its own is not a guarantee of clinical safety or usefulness. Two systems may agree on message structure but still disagree on meaning. A field called “problem list” might contain chronic diagnoses in one system and acute complaints in another. A field labelled “allergies” could contain intolerances in one record and only IgE-mediated reactions in another. Here we start to see the limit of syntactic interoperability: it enforces structure, not interpretation.
Health systems have historically prioritised syntactic interoperability because it is more straightforward to define, test, regulate, and procure. It is easier to say “System X must be able to send and receive FHIR Patient resources” than it is to say “System X must understand that this FHIR Observation represents a potassium level measured in mmol/L.” For this reason, many integration programmes have succeeded in achieving technical connectivity while still struggling to deliver reliable, joined-up clinical meaning.
Despite its limitations, syntactic interoperability remains foundational. Without it, nothing moves. It allows data exchange between hospital EPRs, GP systems, social care platforms, and personal health apps. It underpins e-prescribing workflows, discharge summaries, diagnostic imaging transfers, and referral management. In short, syntactic interoperability is necessary for digital health to function at scale—but it is not sufficient for high-quality care coordination or analytics.
Semantic interoperability goes beyond structure and focuses on meaning. When two systems achieve semantic interoperability, they can not only exchange data and parse it successfully, but also interpret it in the same way. The receiving system understands the clinical intent and context of the data to a degree that allows it to act on that data safely and automatically.
In practice, semantic interoperability depends on shared terminologies, ontologies and coding systems. Instead of relying on free-text, inconsistent labels, health data is represented using controlled vocabularies and standard clinical concepts. These define not just labels but also relationships between concepts—hierarchies, synonyms, and allowed values. Common terminologies include SNOMED CT for conditions, LOINC for laboratory tests, ICD for classifications, and dm+d or RxNorm for medicines. By encoding data using these structured vocabularies, two systems can interpret diagnoses, lab results or medications in the same clinically meaningful way.
Consider a simple example involving an allergy. System A records that a patient is “allergic to penicillin” and encodes it using a SNOMED CT concept denoting penicillin hypersensitivity. System B, upon receiving this data, recognises that this concept falls under the broader class of beta-lactam antibiotic allergies and can therefore trigger alerts to prescribers attempting to order amoxicillin. That is semantic interoperability: the structured meaning is preserved.
Another example is in lab results. Suppose a GP system sends an Observation representing a creatinine result. Syntactic interoperability ensures the field exists and the value is transmitted. Semantic interoperability ensures that the receiving system knows that the test was serum creatinine, understands the units (µmol/L vs mg/dL), and can safely feed that value into algorithms estimating kidney function. Without this shared meaning, patient safety can be compromised.
Semantic interoperability also enables accurate analytics and population health insights. Without semantic alignment, data used for predictive models or public health research can be misleading. A dashboard counting “heart failure” might differ across systems if one includes acute fluid overload while another only includes chronic congestive heart failure. This can distort clinical decisions, resource allocation, and public health policy.
At its core, semantic interoperability turns data into knowledge. It allows systems to interpret information contextually and apply it meaningfully. It supports continuity across care settings, informed decision-making, and trustworthy AI-driven healthcare analytics.
Although both are essential, they are often conflated. Understanding their distinctions helps digital health teams avoid assuming that one delivers the other.
Here are the key differences between the two forms of interoperability:
The two are complementary layers, not alternatives. Syntactic interoperability is the foundation ensuring reliable data exchange, while semantic interoperability ensures that the exchanged data can safely drive patient care and system intelligence.
Semantic interoperability is often described as “the hard part” of digital health transformation. Health data is inherently messy and variable across settings. Two clinicians can describe the same case differently, and two systems can capture data for distinct purposes. This is not just a technical challenge but a question of clinical safety and trust.
From a patient safety perspective, semantic alignment reduces the risk of information loss in translation. Allergy data is a clear example, but so too are advance care plans, safeguarding flags, and medication lists. When a frail patient is seen by urgent care at night, clinicians need not only to know that “there is an advance care plan” but also understand the details—resuscitation status, ceiling of care, and preferred place of care. Syntactic interoperability might deliver a PDF; semantic interoperability makes that information computable, surfacing real-time alerts that can prevent harmful decisions.
Care coordination also depends on shared meaning. Integrated care systems bring together GPs, hospitals, mental health services, community teams and social care. This collaboration works only if each actor can interpret the others’ information correctly. A mental health note about crisis risk or safeguarding must mean the same thing to emergency clinicians as it does to social workers. Semantic interoperability ensures these nuances survive system boundaries.
It also underpins high-quality analytics. Without consistent coding, performance metrics and population health dashboards can be biased. Differences in how conditions are coded can make one hospital appear less safe or another more efficient simply because of documentation variation. Semantic alignment ensures fairness and accuracy in quality measurement and funding models.
Finally, semantic interoperability supports research and innovation. Machine learning models and predictive algorithms depend on clean, well-labelled data. When semantic consistency is missing, training data becomes unreliable, and AI outputs risk bias or error. In short, semantic interoperability is the foundation for safe and equitable digital health innovation.
Achieving full interoperability is not a technical sprint but a long-term transformation. Health IT estates are fragmented, legacy-heavy, and varied in maturity. Systems have evolved to serve specific clinical domains and local needs, often using proprietary designs. Bringing these into a unified, learning health ecosystem requires coordinated action across technology, governance and culture.
The first step is agreeing on and enforcing consistent technical standards for exchange. This is the foundation of syntactic interoperability. Defining message formats, payloads, and APIs ensures any system can “plug in” to the wider ecosystem. Strong procurement standards can prevent the re-emergence of proprietary data silos that lock patient data into vendors’ ecosystems.
However, syntactic alignment without semantic alignment simply moves ambiguous data faster. Therefore, health systems must also define detailed clinical coding expectations. This includes specifying which terminologies apply to which data elements, how detailed entries should be, and in what context. For instance, SNOMED CT might be used for problem lists, dm+d for medications, and LOINC for lab results. Moreover, user interfaces must encourage structured, coded data capture rather than free text.
Interoperability also requires governance and stewardship. Clinical concepts evolve, coding systems update, and service models change. Semantic interoperability must be curated actively. Data stewards, information governance leads, and clinical informaticians must continually maintain mappings, resolve ambiguities, and guide local implementations to avoid drift over time.
Change management is equally critical. Clinicians are under time pressure, and structured data entry can be burdensome if poorly designed. Interfaces must align with real workflows and provide tangible benefits—such as auto-completing discharge letters or supporting medication safety alerts—to justify the effort of structured input. When clinicians experience value, adoption rises.
Funding models also shape success. Interoperability benefits often accrue system-wide rather than to a single organisation. Policymakers and commissioners must design incentives so that all participants see returns from better data quality and shared standards.
Legacy systems pose an additional challenge. Many core systems pre-date modern interoperability standards, storing vital data in PDFs or proprietary formats. Replacing them overnight is unrealistic. Instead, middleware, terminology services, and interface engines can help bridge gaps. Interface engines translate between old and new message formats (ensuring syntactic interoperability), while terminology services map local codes to national vocabularies (enabling semantic interoperability).
The most successful strategies are incremental and clinically led. Instead of pursuing universal interoperability in one leap, health systems can begin with high-value use cases—such as medicines reconciliation or allergy sharing—and ensure both syntactic and semantic robustness there. Once proven, the same approach can scale to additional pathways and organisations, building confidence and momentum.
Syntactic interoperability and semantic interoperability are often described as layers of the same stack, but the difference between them is far more than technical nuance. Syntactic interoperability ensures that health data can be exchanged and read by systems using predictable formats. It is the plumbing that enables connectivity. Semantic interoperability ensures that this exchanged data carries consistent meaning and can safely drive care decisions. It is the understanding that transforms connectivity into clinical intelligence.
Digital health strategies that stop at syntactic interoperability risk creating the illusion of integration—where systems can exchange files but humans still have to interpret every detail manually. True transformation requires semantic interoperability: shared understanding, consistent coding, and safe reuse of information across boundaries.
When both layers are in place, data follows the patient, supports clinicians, empowers analytics, and builds a truly learning health system. The result is care that is safer, more coordinated, and more intelligent—delivering not just digital connection, but digital comprehension.
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