EHR Integration Guide: Epic, Athena, and Cerner

EHR integration is the engine of clinical data exchange; the connective tissue that allows lab results, medication lists, imaging orders, and care summaries to flow seamlessly between the systems clinicians rely on. In a landscape where Epic alone holds 42.3% of the acute care hospital market, with Oracle Health (Cerner) at 22.9% and Athenahealth dominating ambulatory settings, most health systems are not running one EHR, they are running several. Getting those platforms to talk to each other is no longer optional. It is both a clinical and financial imperative.

Key Takeaways

• Multi-EHR environments are the norm, not the exception: Mergers, acquisitions, and specialty workflows mean most health systems operate across Epic, Cerner, Athenahealth, and legacy platforms simultaneously, making vendor-agnostic EHR integration essential.

• FHIR is accelerating, but HL7 v2 still runs the show: While 71% of countries report active FHIR usage and adoption is climbing fast, the majority of real-time clinical data exchange (labs, orders, ADT) still moves over HL7 v2 interfaces.

• Routine interoperability is the new benchmark: According to ONC data, 70% of U.S. hospitals now engage in all four domains of interoperable exchange (send, receive, find, integrate), up from just 46% in 2018.

• Integration strategy must be vendor-agnostic: The best integration architectures normalize data across EHR platforms rather than building point-to-point connections that break at scale.

Why EHR Integration Drives Clinical Performance

Having an EHR installed and having your EHR integrated are two very different things. The global EHR market is valued at roughly $29.8 billion in 2025 and is projected to exceed $52 billion by 2034. However, that investment only pays off when data moves fluidly across systems.

The real cost of fragmented EHR environments appears in duplicated lab orders, missed medication interactions, and care teams making decisions without a complete clinical picture. ONC research shows that hospitals with routine interoperability report significantly higher rates of clinicians accessing and using external patient data at the point of care; 70% compared to just 18% at hospitals that rarely exchange data.

Bottom line: EHR integration is not merely an IT project. It is a care quality multiplier.

The Reality of Multi-EHR Environments

Why Health Systems Run Multiple Platforms

If you're operating in a health system that spans hospitals, ambulatory clinics, specialty groups, and post-acute facilities, you're almost certainly running more than one EHR. Epic won nearly 70% of all hospital EHR decisions in 2024, but that does not mean every facility under a single system runs Epic. M&A activity, specialty-specific workflows, and legacy contracts create multi-vendor environments that persist for years.

Consider a large integrated delivery network that runs Epic for inpatient care, Athenahealth for its ambulatory network, and legacy Cerner (now Oracle Health) instances from a recent acquisition. Each system stores patient data differently, uses distinct terminologies, and exposes different APIs.

Where Data Silos Form

The most common integration gaps occur between:

• Inpatient and ambulatory systems: hospital discharge summaries not reaching primary care physicians

• Lab information systems and the EHR: results trapped in an LIS without flowing into the ordering provider's chart

• Imaging systems (PACS/RIS) and the clinical record: radiology reports disconnected from the encounter

• Legacy systems awaiting decommission: archived patient data that clinicians still need but can't easily access

Pro Tip: Before mapping integration workflows, audit every active data source. Health systems consistently undercount how many clinical applications are still in production: sometimes by hundreds.

Vendor-Agnostic Integration Principles

Normalize Before You Connect

The most resilient EHR integration strategies avoid building one-off connections between System A and System B. Instead, they establish a normalization layer that translates data from any source into a common structure. This means:

• Standardized patient identifiers across systems using an enterprise master patient index (EMPI)

• Unified terminology mapping: converting between SNOMED, ICD-10, LOINC, and CPT codes regardless of source

• Consistent document formats: whether the source sends a CCD, a C-CDA, or a FHIR Bundle, the integration layer normalizes it

Decouple Integration from Individual EHRs

Many teams attempt to solve integration challenges by building direct Epic-to-Cerner interfaces. While this may address an immediate need, it introduces technical debt the moment another EHR enters the ecosystem. A vendor-agnostic middleware approach, such as an integration engine or a data enablement platform, absorbs the complexity so downstream consumers receive normalized, unified data.

Key Insight: Organizations realizing the fastest ROI from EHR integration treat data normalization as a platform capability, not a one-off project. Clearsense's data enablement platform, for example, integrates data from multiple EHR sources into a unified environment, enabling clinicians to view a comprehensive patient record without logging into separate applications.

Common EHR Integration Workflows

Lab Results (ORU Messages)

Lab integration is typically the highest-volume, most time-sensitive workflow. Results flow from a laboratory information system into the EHR as HL7 v2 ORU (Observation Result Unsolicited) messages. Critical requirements include speed, accurate patient matching, and proper LOINC mapping to ensure correct display in the chart.

Medication Management (RDE/RDS Messages)

Prescription and dispensing workflows rely on HL7 v2 RDE (Pharmacy/Treatment Encoded Order) and RDS (Pharmacy/Treatment Dispense) messages, along with NCPDP SCRIPT for e-prescribing. Integration must account for formulary differences and cross system drug interactions.

Orders and Imaging (ORM/OMG Messages)

Computerized provider order entry generates ORM messages that route to ancillary systems: lab, radiology, pathology. Imaging orders trigger additional workflows through DICOM and IHE profiles, connecting the EHR to PACS and radiology information systems.

ADT (Admit, Discharge, Transfer)

ADT messages formthe backbone of real-time patient tracking. These HL7 v2 A01 (admit), A03 (discharge), and A02 (transfer) events trigger downstream workflows across the entire care continuum, from bed management to billing to care coordination notifications.

Data Formats in Practice: HL7, FHIR, and CCD

HL7 v2: The Workhorse

Despite being decades old, HL7 v2 remains the dominant format for real-time data exchange. It is pipe-delimited and not particularly elegant, but it is ubiquitous and deeply embedded in lab instruments, pharmacy systems, and radiology departments. Most production EMR integrations still run on HL7 v2 interfaces.

FHIR: The Future (and Increasingly the Present)

FHIR R4 adoption continues to accelerate. The 2025 State of FHIR survey found that 54% of respondents expect a strong increase in FHIR adoption in the coming years, up from 39% in 2024. Federal mandates under the 21st Century Cures Act require certified EHRs to support FHIR APIs, and TEFCA now supports FHIR-based exchange at the national level.

In practice, FHIR excels in patient-facing applications, bulk data export, and API-driven integrations. Athenahealth's marketplace includes more than 800 API-enabled solutions with FHIR R4 support. Epic's FHIR APIs power its App Orchard ecosystem. Oracle Health continues investing heavily in FHIR through its cloud infrastructure strategy.

CCD and C-CDA: The Document Layer

Continuity of Care Documents (CCDs) and Consolidated Clinical Document Architecture (C-CDA) documents manage structured care-transition summaries. Upon discharge or referral, a C-CDA packages demographics, problem lists, medications, allergies, and recent results into a structured XML document that the receiving system can parse and integrate.

Pro Tip: FHIR and HL7 v2 are not mutually exclusive. The strongest integration architectures leverage HL7 v2 for high-volume real-time feeds and FHIR for API-based access, applications, and bulk data. Plan for coexistence rather than replacement.

Common EHR Integration Mistakes to Avoid

Mistake 1: Building Point-to-Point Connections

Each new point-to-point interface increases system complexity. With three systems, you need three connections. With ten, you need forty-five. A centralized integration engine or data platform eliminates this scaling constraint.

Mistake 2: Ignoring Legacy Data

When decommissioning a legacy EHR, the data remains clinically and legally relevant. Clinicians still require access. Clearsense specializes in active data archival, preserving and unifying legacy clinical data so it remains accessible within the clinician's current workflow. One large U.S. health system retired nearly 800 applications through this approach, realizing over $65 million in net annual savings.

Mistake 3: Treating Integration as a One-Time Project

Healthcare system integration is ongoing. Regulatory updates, EHR version changes, M&A activity, and evolving standards such as USCDI and FHIR R5 require ongoing monitoring and refinement of the integration layer.

Frequently Asked Questions

What is EHR integration?

EHR integration connects electronic health record systems with clinical, financial, and operational applications so patient data flows automatically and accurately across the care continuum. It enables clinicians to access a complete patient picture regardless of where care was delivered.

How does Epic integration differ from Cerner or athenahealth integration?

Each vendor exposes different APIs and interface standards. Epic uses its App Orchard and FHIR APIs; Oracle Health (Cerner) leverages its Millennium platform and Open APIs; and Athenahealth offers over 800 RESTful API endpoints through its developer portal. A vendor-agnostic integration strategy normalizes these differences.

What data formats are used for clinical data exchange?

Primary formats include HL7 v2 messaging (for real-time feeds like labs, orders, and ADT), FHIR R4 (for API-based access and modern apps), C-CDA documents (for care transition summaries), and NCPDP SCRIPT (for e-prescribing). Most health systems use a combination of all four.

How long does an EHR integration project typically take?

Timelines vary significantly. A single interface, such as a lab feed, can take 6 to 12 weeks. Enterprise-wide healthcare system integration involving multiple EHRs, legacy archives, and data normalization can span 12 to 24 months or more depending on scope and organizational complexity.

Is FHIR replacing HL7 v2?

Not yet in practice, though FHIR adoption is accelerating rapidly. The 2025 State of FHIR survey reports that 71% of countries now have active FHIR use cases. However, HL7 v2 remains the backbone for high-volume, real-time clinical data exchange and will coexist with FHIR for years to come.

What role does TEFCA play in EHR integration?

The Trusted Exchange Framework and Common Agreement (TEFCA) is a federal framework that removes barriers to nationwide health information exchange. It establishes a universal floor for data sharing through Qualified Health Information Networks (QHINs), supporting treatment, public health, and benefits determination use cases.

Sources

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[2] Fortune Business Insights: Electronic Health Records Market Size & Share, 2034. https://www.fortunebusinessinsights.com/electronic-health-records-ehr-market-102660

[3] Firely / HL7 International: The State of FHIR in 2025: Growing Adoption and Evolving Maturity. https://fire.ly/blog/the-state-of-fhir-in-2025/

[4] ONC (Office of the National Coordinator): Interoperable Exchange of Patient Health Information Among U.S. Hospitals: 2023. https://www.healthit.gov/data/data-briefs/interoperable-exchange-patient-health-information-among-us-hospitals-2023

[5] ONC / HealthIT.gov: Raising the Bar on Interoperability. https://www.healthit.gov/buzz-blog/health-information-exchange-2/raising-the-bar-on-interoperability-a-decade-of-data-show-that-sometimes-isnt-good-enough

[6] Dark Daily / KLAS Research: Epic Expands EHR Market Share as Rivals Lose Customers. https://www.darkdaily.com/2025/06/04/epic-expands-ehr-market-share-as-rivals-lose-customers/

[7] athenahealth: API Marketplace Partners with Over 800 Solutions. https://www.athenahealth.com/solutions/marketplace-partners

[8] athenahealth: Developer Resources: APIs, Interfaces & More. https://www.athenahealth.com/developer-portal

[9] ONC / HealthIT.gov: Trusted Exchange Framework and Common Agreement (TEFCA). https://www.healthit.gov/topic/interoperability/policy/trusted-exchange-framework-and-common-agreement-tefca

[10] Clearsense: Healthcare Data Integration Solutions. https://clearsense.com/solutions

[11] Clearsense / KLAS: Featured in KLAS Emerging Insights Case Study. https://clearsense.com/press-news/clearsense-featured-in-klas-emerging-insights-case-study-for-powering-the-largest-and-most-impactful-application-rationalization

[12] Clearsense: Earns NCQA Validated Data Stream Status for FHIR. https://clearsense.com/press-news/ncqa-validation-2