LOINC Terms and SNOMED CT Observable Entities

LOINC Terms are primarily represented within the Observable Entity hierarchy of SNOMED CT for several reasons. Firstly, LOINC terms predominantly capture observable clinical phenomena, such as laboratory test results, measurements, observations, and assessments, which align closely with the scope of observable entities in SNOMED CT. This conceptual alignment ensures that many LOINC terms fit naturally within SNOMED CT’s structure, facilitating their integration into the broader clinical terminology framework. Additionally, LOINC terms often require a detailed representation of properties, scales, units, methods, and other attributes associated with clinical observations.

However, it is important to note that certain areas of LOINC, such as document-related terms or results of observations, may be more appropriately represented in other SNOMED CT hierarchies.

SNOMED CT’s structured framework supports this flexible approach, enabling precise representation of LOINC concepts and ensuring that all relevant attributes are accurately documented.

LOINC Parts as SNOMED CT Attribute Values

LOINC Parts are represented as SNOMED CT attribute values to enable the definition of LOINC Terms using SNOMED CT's logical foundation while retaining the meaning represented in LOINC. This approach ensures a granular representation of defining attributes like properties, scales, methods, components, and systems, facilitating precise documentation of clinical concepts. Additionally, leveraging SNOMED CT's semantic framework maintains consistency, accurately associating each component with the appropriate context and contributing to standardized clinical information representation.

Development Process

To express LOINC terms as SNOMED CT concepts, a structured process was established. This ensures efficient development efforts resulting in content with a high level of consistency and accuracy throughout.

Here's a breakdown of the process and its objectives:

1. Utilizing latest LOINC Parts: The process begins by utilizing the latest list of LOINC Parts, which are relevant for the preview.

2. Mapping LOINC Parts: LOINC Terms are modeled based on various LOINC Parts, with specific instructions provided for each property type.

3. Assigning Attributes: Attributes necessary for modeling LOINC Terms are determined based on the LOINC Property type. Templates are provided for different scenarios, such as observable with component, observable with component and relative to, observable with inheres in, and susceptibility observable. These templates and their criteria for selection are described in the sub-pages listed below.

4. Modeling: LOINC axes (Property, Scale, Time, System, Method, Component, etc.) are mapped to appropriate SNOMED CT attributes.

5. Terming and Description: Fully Specified Name (FSN) and a SNOMED-compliant acceptable description are created based on a defined set of rules.

6. Validation: Where a mapped attribute is not available for a given LOINC Part, depending on the axes it may be that the concept can be considered valid (although primitive and not fully defined), or in the case of some essential part like 'component', the concept cannot be considered fit for use and is suppressed - not included in the output of the process.

7. Creation and Review: New observable entity concepts are created in the LOINC Extension project (and updates are made to previously modeled content as required), and they undergo quality assurance (QA) review, classification, validation, etc., to ensure accuracy and consistency.

8. Modeling Examples: Examples are provided to illustrate how the content should be structured and how LOINC identifiers and descriptions should be integrated into SNOMED concepts.

Conversion of LOINC Terms to SNOMED CT Concepts - A Templated Solution

The following pages describe the applied templates and provide examples.

• 4.1 Alternate Identifiers - Identifying LOINC Terms in SNOMED CT
• 4.2 Template Based Content Creation
  • 4.2.1 Quality Observable with Component
  • 4.2.2 Quality Observable with Inheres in (System, no Component)
  • 4.2.3 Quality Observable with Inheres In
  • 4.2.4 Quality Observable with Process
  • 4.2.5 Quality Observable with Ratio
  • 4.2.6 Quality Observable with Relative to
  • 4.2.7 Quality Observable with Susceptibility
  • 4.2.8 Quality Observable with Process (No Process output, With Time aspect)
• 4.3 Orderable and Observable LOINC Terms

Additional SNOMED CT Concepts Required

The driving philosophy of the SNOMED LOINC Extension is to faithfully translate LOINC content into a SNOMED CT representation without adding, removing or modifying any term, and without the need for additional manual intervention.   However, there are a small number of additional SNOMED CT concepts that were required in order to make the transition from a LOINC structure to a SNOMED one: