How Healthcare Providers Are Extracting Legacy Patient Data Logic into Modern UIs

The $3.6 trillion global technical debt isn't just a line item on a balance sheet; in healthcare, it’s a barrier to patient care. 70% of legacy modernization projects fail or exceed their timelines because organizations treat them as "Big Bang" rewrites. When you are dealing with decades-old Electronic Health Records (EHR) or claims processing systems, you aren't just fighting old code—you are fighting the "documentation gap." With 67% of legacy systems lacking any meaningful documentation, architects are forced into "code archaeology," spending months trying to understand business logic before a single line of modern code is written.

TL;DR: How healthcare providers are accelerating modernization by using Replay’s visual reverse engineering to extract patient data logic into documented React components, reducing rewrite timelines from 18 months to just weeks.

The High Cost of Manual "Archaeology" in Healthcare#

For most healthcare CTOs, the status quo is a trap. You have a monolithic patient portal or a legacy billing system built in 2004. The original developers are gone. The business logic—rules for patient eligibility, complex HL7 data transformations, and state-specific compliance checks—is buried in a "black box."

The traditional approach is to assign a team of senior engineers to manually audit the codebase. This takes an average of 40 hours per screen just to document the requirements. If your system has 200 screens, you are looking at 8,000 hours of manual labor before you even start building the modern UI.

The Modernization Matrix: Comparing Approaches#

💰 ROI Insight: By moving from manual documentation to Replay’s automated extraction, enterprise teams reduce the time-per-screen from 40 hours to 4 hours—a 90% reduction in discovery costs.

How Healthcare Providers Are Using Replay to Extract Logic#

Modernization is no longer about reading 50,000 lines of legacy Java or COBOL. It’s about observing the system in action. Replay allows architects to record real user workflows—like a nurse entering patient vitals or a billing specialist processing a claim—and converts those visual interactions into clean, documented code.

Step 1: Visual Recording of the "Golden Path"#

Instead of digging through a database schema, an architect records the legacy application while performing a specific task. Replay captures the state changes, network requests, and DOM mutations. This becomes the "source of truth."

Step 2: Logic Extraction and Component Generation#

Replay’s AI Automation Suite analyzes the recording to identify the underlying business logic. It separates the "what" (patient data) from the "how" (the legacy UI).

Step 3: Generating Modern React Components#

Once the logic is identified, Replay generates a modern React component that mirrors the legacy functionality but utilizes a modern tech stack. This isn't a "transpilation" of old code; it's a reconstruction of the intent.

typescript
// Example: React component generated by Replay from a legacy Patient Vitals screen
// The logic for calculating BMI and flagging high BP is preserved from the recording.

import React, { useState, useEffect } from 'react';
import { Alert, Card, Input, Button } from '@/components/ui'; // From Replay Library

interface PatientVitalsProps {
  patientId: string;
  onSave: (data: VitalsData) => void;
}

export const PatientVitalsModern: React.FC<PatientVitalsProps> = ({ patientId, onSave }) => {
  const [vitals, setVitals] = useState({
    systolic: 0,
    diastolic: 0,
    weightKg: 0,
    heightCm: 0
  });

  // Business Logic extracted from legacy 'vitals_calc.js'
  const calculateBMI = (w: number, h: number) => (w / ((h / 100) ** 2)).toFixed(2);
  const isHypertensive = vitals.systolic > 140 || vitals.diastolic > 90;

  return (
    <Card title="Patient Vitals Entry">
      <div className="grid grid-cols-2 gap-4">
        <Input 
          label="Systolic BP" 
          type="number" 
          onChange={(e) => setVitals({...vitals, systolic: +e.target.value})} 
        />
        <Input 
          label="Diastolic BP" 
          type="number" 
          onChange={(e) => setVitals({...vitals, diastolic: +e.target.value})} 
        />
      </div>
      
      {isHypertensive && (
        <Alert variant="danger">
          ⚠️ Warning: Patient exceeds hypertensive threshold.
        </Alert>
      )}

      <div className="mt-4">
        <strong>Calculated BMI:</strong> {calculateBMI(vitals.weightKg, vitals.heightCm)}
      </div>

      <Button onClick={() => onSave(vitals)}>Sync to EHR</Button>
    </Card>
  );
};

Bridging the Gap: API Contracts and E2E Tests#

The biggest risk in healthcare modernization is data integrity. If the new UI doesn't talk to the legacy backend exactly like the old one did, you risk corrupting patient records.

Replay doesn't just generate UI; it generates the API Contracts and E2E Tests required to ensure parity. By observing the network traffic during the recording phase, Replay creates a blueprint of the legacy API, even if that API was never documented.

Step 4: Blueprinting the Legacy API#

Replay identifies every endpoint hit during the user session and generates a Swagger/OpenAPI specification. This allows your backend team to build a modern middleware or wrapper without guessing at the payload structure.

yaml
# Generated by Replay Blueprint: Legacy Patient API
openapi: 3.0.0
info:
  title: Legacy EHR Integration
  version: 1.0.0
paths:
  /api/v1/patient/vitals:
    post:
      summary: Extracted from 'Save Vitals' workflow
      requestBody:
        content:
          application/json:
            schema:
              type: object
              properties:
                p_id: { type: string }
                sys_bp: { type: integer }
                dia_bp: { type: integer }
                ts: { type: string, format: date-time }
      responses:
        '200':
          description: Success

⚠️ Warning: In regulated environments, "guessing" at API contracts leads to catastrophic data loss. Always use a generated contract as your baseline for integration testing.

Security and Compliance in Regulated Environments#

Healthcare providers cannot move data to the cloud for analysis without strict safeguards. This is where most AI-driven tools fail. Replay was built for the constraints of Financial Services and Healthcare.

• •SOC2 & HIPAA Ready: Data handled by Replay follows stringent encryption and privacy protocols.
• •On-Premise Availability: For organizations with the highest security requirements, Replay can be deployed entirely within your own VPC or firewalled environment.
• •Data Masking: During the "Recording" phase, Replay can automatically mask PII (Personally Identifiable Information) so that developers are working with structural data, not actual patient records.

The "Strangler Fig" 2.0: Modernizing Screen by Screen#

The "Big Bang" rewrite is dead. The future is an iterative extraction. Using Replay, healthcare providers are adopting a "Screen-by-Screen" modernization strategy:

1. •Identify the highest-pain screen (e.g., Patient Intake).
2. •Record the workflow using Replay.
3. •Extract the React components and business logic.
4. •Deploy the modern screen within the legacy shell (using a micro-frontend approach).
5. •Repeat for the next highest-value workflow.

This approach ensures that you provide value to users in weeks, not years. It also allows you to manage technical debt incrementally rather than letting it accumulate into a $3.6 trillion problem.

📝 Note: This methodology is particularly effective for systems where the backend logic is stable but the frontend is unusable or incompatible with modern browsers (e.g., IE11 dependencies).

Frequently Asked Questions#

How does Replay handle complex business logic that isn't visible in the UI?#

Replay captures the "state transitions." If a button click triggers a complex calculation that then updates five different fields, Replay observes those changes and the data flow. While it doesn't "read" the backend COBOL code, it documents the observable behavior of that code, which is what is required to replicate the logic in a modern environment.

Does Replay work with legacy technologies like Silverlight, Flash, or Mainframe Green Screens?#

Yes. Because Replay uses visual reverse engineering and DOM/network capture, it can extract logic from any web-based legacy system, including those running in compatibility modes. For terminal-based systems, Replay uses OCR and state-mapping to build the blueprint.

How much manual coding is still required?#

Replay handles approximately 70% of the heavy lifting—documentation, component scaffolding, and API contract generation. Your developers still handle the final 30%: styling to match your specific design system, complex edge-case handling, and final integration. This shifts their role from "archaeologists" to "architects."

What happens to the documentation once the project is over?#

The documentation generated by Replay (The Library and Flows) lives on as a living asset. Unlike a PDF document that becomes obsolete the day it's written, Replay's documentation is tied to the code and components, providing a permanent map of your new architecture.

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Ready to modernize without rewriting? Book a pilot with Replay - see your legacy screen extracted live during the call.