Electronic Health Record System Design: Epic and Cerner-inspired Interview Questions

Problem Statement

Designing Electronic Health Record (EHR) systems requires balancing complex data models, interoperability standards, and strict compliance requirements. Technical interviews at companies like Epic and Cerner challenge candidates to create architectures that handle diverse medical data while ensuring seamless integration between systems, exceptional performance, and strict HIPAA compliance.

EHR System Architecture Overview

A modern EHR system consists of multiple integrated components that work together to provide comprehensive patient care functionality:

When Epic Systems asks candidates to "Design an electronic health record (EHR) system considering HIPAA compliance," this high-level architecture forms the foundation for a comprehensive answer.

Data Model and Domain Design

The heart of an EHR system is its clinical data model. A well-designed model must represent complex medical relationships while enabling efficient querying:

Domain-Driven Design Approach

EHR systems benefit from a domain-driven design approach with bounded contexts:

When designing EHR systems, clearly separating these bounded contexts improves maintainability while allowing specialized teams to work on different components.

Interoperability Implementation

Cerner interviews often focus on interoperability challenges. A robust EHR must integrate seamlessly with other healthcare systems:

FHIR Implementation Strategy

Modern EHR systems typically implement FHIR (Fast Healthcare Interoperability Resources) for standardized data exchange:

1// Example FHIR patient resource creation
2function createPatientResource(demographics) {
3  return {
4    resourceType: "Patient",
5    id: generateId(),
6    identifier: [{
7      system: "http://hospital.org/mrn",
8      value: demographics.mrn
9    }],
10    name: [{
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Data Consistency and Transaction Management

Cerner often asks about data integrity in distributed healthcare systems. EHR transactions must maintain ACID properties despite complexity:

Consistency Patterns

When Epic interviews ask about data consistency in EHR systems, focus on these patterns:

1. Saga Pattern: Coordinate complex medical workflows across services with compensating transactions
2. Event Sourcing: Maintain complete audit history of all healthcare data changes
3. CQRS: Separate read and write models for efficient clinical data access patterns
4. Optimistic Concurrency: Enable collaborative documentation with version control

Scalability and Performance

Epic Systems frequently asks candidates about handling high patient volumes. EHR systems must scale to support large healthcare networks:

Performance Optimization Strategies

1. Read-Heavy Optimizations

   • Clinical data presentation caching
   • Pre-computed clinical quality measures
   • Materialized patient summary views

2. Write Efficiency

   • Batch laboratory result processing
   • Asynchronous document creation
   • Optimistic locking for concurrent documentation

3. Query Performance

   • Specialized clinical indexes
   • Temporal data partitioning
   • Smart pagination for large result sets

High Availability and Disaster Recovery

When Cerner asks about hospital system reliability, your design must address continuous operation requirements:

Downtime Strategies

EHR systems require specialized downtime strategies for when full system access is unavailable:

1. Read-Only Mode: Allow clinical data viewing when write operations fail
2. Local Caching: Enable critical operations with locally cached data
3. Downtime Forms: Provide paper-based alternatives with later reconciliation
4. Progressive Degradation: Maintain core clinical functions even when peripheral services fail

Real-time Hospital Bed Management

A common interview question at Optum is "How would you design a real-time hospital bed management system?" This requires specialized architecture:

Real-time Implementation

The key technical challenge is maintaining real-time state across distributed systems:

1// WebSocket-based bed status updates
2function setupBedStatusSocket(hospitalUnit) {
3  const socket = new WebSocket(`wss://api.hospital.org/beds/${hospitalUnit}`);
4  
5  socket.onmessage = (event) => {
6    const update = JSON.parse(event.data);
7    
8    // Process different bed events
9    switch(update.type) {
10      case 'ASSIGNMENT':
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Patient Appointment Scheduling System

Epic Systems often asks candidates to "Design a patient appointment scheduling system that can handle millions of concurrent users." This requires specialized architecture:

Scaling Strategies

To handle millions of concurrent users, implement these scaling techniques:

1. Read Replication: Distribute appointment availability reads across replicas
2. Write Partitioning: Partition appointment writes by location/department
3. Caching Layer: Cache common availability patterns
4. Asynchronous Processing: Queue non-immediate operations
5. Regional Deployment: Deploy regionally to minimize latency

Key Takeaways

• Domain-Driven Design: Structure EHR systems around clinical domains and bounded contexts
• Interoperability First: Build standardized integration points using FHIR and HL7
• Data Consistency: Implement distributed transaction patterns appropriate for healthcare
• High Availability: Design for zero downtime with redundancy and failover mechanisms
• Real-time Capabilities: Use event-driven architecture for time-sensitive clinical workflows

EHR System Component Architecture Templates

Download our comprehensive EHR system design framework with component architecture templates for your next HealthTech interview.

The framework includes:

• Core EHR component diagrams
• FHIR implementation patterns
• HL7 integration templates
• Scalability models for different hospital sizes
• Availability zone design patterns

Download Framework →

Sources

1. HL7 FHIR Architecture Overview: https://www.hl7.org/fhir/architecture.html
2. Healthcare Information and Management Systems Society (HIMSS): https://www.himss.org/resources-interoperability
3. ONC Health IT Certification Program: https://www.healthit.gov/topic/certification-ehrs
4. Epic Systems Architecture Patterns: Epic Systems Engineering Blog
5. Cerner Implementation Best Practices: Cerner Health Conference Proceedings