Demo - The specification is a demo of MERT. For a full list of available versions, see the Directory of published versions

Terminology

This section defines terminology usage, binding expectations, and coding system requirements for the MERT specification.

MERT prioritizes preservation of clinical meaning while recognizing variability across heterogeneous EMR systems.

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1. Terminology Philosophy

MERT distinguishes between:

• Required bindings – The element SHALL use codes from the specified ValueSet.
• Extensible bindings – The element SHOULD use codes from the specified ValueSet. If not possible, an alternative code MAY be used, but clinical meaning SHALL be preserved.
• Preferred bindings – Use of the specified ValueSet is encouraged but not mandatory.

Where structured coding cannot be preserved during import, the Receiver SHALL preserve the human-readable clinical meaning.

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2. External Code Systems

MERT profiles reference established terminology systems, including but not limited to:

• LOINC
• SNOMED CT
• UCUM
• HL7-defined CodeSystems
• Jurisdiction-specific medication or provider identifiers (where applicable)

Systems SHALL preserve source codings when present.

Receivers MAY map codes to local coding systems but SHALL NOT discard the clinical meaning.

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3. MERT-Defined ValueSets

MERT defines constrained ValueSets to promote safe and predictable exchange.

Each ValueSet definition SHALL include:

• Canonical URL
• Binding strength
• Intended element path(s)
• Allowed codes
• Status (active/draft)

Where MERT constrains a base FHIR ValueSet to a subset, only the enumerated codes SHALL be permitted when binding strength is Required.

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4. Text and Display Expectations

For CodeableConcept elements:

• coding.display SHOULD be populated when available.
• CodeableConcept.text SHOULD be populated when human-readable meaning is clinically relevant.
• If structured coding cannot be interpreted by the Receiver, human-readable meaning SHALL be preserved.

For Quantity elements:

• Units SHALL use UCUM where specified by binding.
• Value + unit pairing SHALL maintain clinical meaning.

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5. Handling Unsupported Code Systems

If the Receiver does not support a source coding system:

• The Receiver SHALL preserve the human-readable meaning.
• The Receiver MAY store the original coding in a structured or raw FHIR store.
• The Receiver SHALL NOT discard clinically relevant data solely due to unsupported coding systems.

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6. Versioning Considerations

MERT does not mandate specific terminology version numbers unless explicitly stated in a profile.

Implementations SHOULD document terminology versions used during validation.

Future MERT releases MAY introduce stricter terminology version constraints.