phi-redaction

PHI Redaction for FHIR Resources

Standard redaction profile for Protected Health Information (PHI) applied on all read paths in the FHIR MCP guardrail stack. This is a technical minimization preview, not a legal Safe Harbor determination.

When to Use This Skill

• You need to understand how PHI is stripped from FHIR resources
• You are building a pipeline that must redact clinical data before AI access
• You need to implement or audit de-identification logic for FHIR

Redaction Rules

All redaction is applied at read time, not at storage time.

Names (HumanName)

• Family name: Kept as-is
• Given names: Truncated to first initial + period (e.g., "John" -> "J.")
• Text: Removed

Identifiers

• Value: Removed (e.g., {"system": "…/us-ssn", "value": "123-45-6789"} -> {"system": "…/us-ssn"})
• System and type: Kept for reference

Addresses

• Line and text: Removed
• City, state, country: Kept (for demographic analysis)

Telecom (Phone, Email)

• Value: Replaced with [Redacted]
• System and use: Kept

Birth Date

• Truncated to year only (e.g., "1985-03-15" -> "1985")

Photos

• Removed entirely from the resource

Text Narratives

• Replaced with: <div xmlns="http://www.w3.org/1999/xhtml">[Redacted]</div>
• Status set to empty

Notes and Comments

• Replaced with [Redacted]

Contained Resources

• All contained resources are redacted recursively

Implementation Pattern (Python)

import json

def apply_redaction(resource):
    """Deep-copy the resource and redact PHI fields."""
    redacted = json.loads(json.dumps(resource))
    _redact_fields(redacted)
    for contained in redacted.get('contained', []):
        if isinstance(contained, dict):
            _redact_fields(contained)
    return redacted

Key implementation notes:

• Always deep-copy before redacting (never modify the stored resource)
• Redact contained resources recursively
• Apply on ALL read paths: direct reads, search results, context envelopes, upstream proxy responses