Introduction

Mapping conventions were created prior to undertaking the initial development of the maps and were revised during the process as experience was gained. The conventions serve to ensure accuracy and consistency in mapping and continue to be applied in the maintenance phase of the production maps. Users of the maps are encouraged to refer to these mapping conventions as a resource for understanding the scope, structure, and intended use of the maps.

Use Cases of the Maps 

The maps were created as part of the WEB-RADR 2 project. The overall purpose of creating the 2 maps was to use the enhanced functionality of the mobile application to facilitate exchange of data between regulatory databases (which use MedDRA) and healthcare databases/electronic health records (which use SNOMED CT). Two maps were developed (from MedDRA to SNOMED CT and SNOMED CT to MedDRA) to support seamless data exchange within the application platform. The sub-set of frequently used terms mapped in the project define a set of key pharmacovigilance terms that need to be linked to their counterparts in either terminology. In addition, a set of COVID-19 related terms were also included in the first production release of the maps to capture important aspects of the pandemic.

For the SNOMED CT to MedDRA map, these key pharmacovigilance concepts when coded in SNOMED CT in an electronic health record (EHR) can be converted to MedDRA for the purpose of adverse event reporting to regulatory authorities or for the purposes of epidemiological research. By using the MedDRA to SNOMED CT map, these same key terms coded in MedDRA representing adverse events, warnings, and other regulatory information can be converted into SNOMED CT so that the information is available for the patient’s record and clinical decision-support.

Timeline

Development of the initial maps based on a sub-set of ~7,400 key pharmacovigilance terms (February-November 2019)

• MedDRA v21.1 
• SNOMED CT version Jan 2019 International edition

Alpha test of the maps

The Alpha testing of this product was conducted from April - September 2020.

First Production release of the maps (April 2021)

• Based on feedback from alpha release and including COVID-19 terms
• MedDRA Version 23.1 (September 2020)
• SNOMED CT January 2021 International edition

Release Schedule

Releases of the maps will occur in April each year and will be based on the September MedDRA release of the preceding year (Version x.1) and SNOMED CT International edition release of January in the current year.

General Mapping Guidance 

Structure and hierarchy 

MedDRA groups its terms in a five-level hierarchy.The Preferred Term (PT) level represents single medical concepts and the Lowest Level Term (LLT) level represents synonyms, lexical variants, and sub-elements. SNOMED CT structure uses concepts as Fully Specified Names (FSNs) with a number of descriptions available (synonyms). Screenshots and examples are intended for illustrative purposes.

SNOMED CT concepts and MedDRA terms are checked against hierarchy placement to determine if concepts/terms are equivalent.

Check SNOMED CT concepts and MedDRA terms against hierarchy placement to determine if concepts/terms are equivalent.

Example

• ›  VitaminD. Direct lexical match but is a test name in MedDRA and a substance in SNOMED CT

• In this case, LLT Vitamin D would be mapped instead to SNOMED CT Vitamin D measurement (procedure) if within scope of the map

Mapping in both directions is to an exact conceptual match for the concept/term

This is defined as the source terminology concept/term and the target terminology concept/term having the same conceptual medical meaning.

Example 1:

• LLT Permanent cardiac pacemaker insertion maps to SNOMED CT Implantation of cardiac pacemaker (procedure)
• SNOMED CT Implantation of cardiac pacemaker (procedure) maps to LLT Cardiac pacemaker insertion

Example 2:

• LLT Emotional lability maps to SNOMED CT Mood swings (finding)
• SNOMED CT Mood swings (finding) maps to LLT Mood swings

Note that while Emotional lability is a synonym of Mood swings in SNOMED CT, in MedDRA, LLT Emotional lability is under PT Affect lability (HLT Affect alterations NEC) and LLT Mood swings is under PT Mood swings (HLT Fluctuating mood symptoms). Both terms are under HLGT Mood disorders and disturbances NEC. The two terminologies use different editorial guidance for their organisation and in some cases such as this one where the structure of SOC Psychiatric disorders is based on DSM-5, closely related terms may be in different parts of the hierarchy. For the purposes of the maps, a pragmatic approach is taken, and concepts/terms are either considered to be exact conceptual matches or unmappable.

Any concepts/terms that are not an Exact Match are flagged as unmappable

This identifies relevant concepts in either terminology that might be missing and are required to provide a more complete mapping. The addition of any new content is discussed by the relevant terminology organisation.

The source term (MedDRA or SNOMED CT) is mapped to the equivalent concept in the target terminology (SNOMED CT or MedDRA)

That same concept in the target terminology then becomes the source for mapping in the reverse direction back to the starting terminology which becomes the target, whilst aiming for the same semantic match.

For example, if a MedDRA term is to be mapped (source), the MedDRA LLT is mapped to an FSN in SNOMED CT (target) to create the MedDRA to SNOMED CT map. Then the same FSN (source) is mapped back to the equivalent concept in MedDRA (target) to create the SNOMED CT to MedDRA map.

Each directional map is independent

Taking the MedDRA to SNOMED CT map as an example, in many instances, the LLT mapped from MedDRA to SNOMED CT will be the same as the LLT when mapped in the reverse direction from SNOMED CT to MedDRA, i.e., LLT 1 to FSN; FSN to LLT 1. In others, the LLT mapped from MedDRA to SNOMED CT will differ from the resulting LLT when mapped in the reverse direction, i.e., LLT 1 to FSN; FSN to LLT 2. This occurs because the two terminologies differ with respect to lexical variants, spellings, etc. However, the clinical meaning of the term/concept should always be the same in both directions. See Principles 1 and 2 for specific examples.

While more than one LLT can map to a single FSN, in the reverse direction going from SNOMED CT to MedDRA, this will always be a 1:1 map. This supports the use case of using SNOMED EHR data to report adverse events without double counting.

Active terms

The maps include active SNOMED CT concepts and current MedDRA LLTs only, i.e., inactive and non-current terms are excluded.

Map terms

Typically the maps use (finding/disorders), (event), (procedure), and (situation with explicit context) concepts in SNOMED CT. However, there may be valid exceptions.

Example

• LLT Infarction maps to FSN Infarct (morphologic abnormality)

The map does not use (substance) concepts in SNOMED CT since the names of drugs and other substances are out of scope of MedDRA.

Unqualified test name terms that indicate simply that a test was performed, e.g., PT Blood glucose, are not included in the maps due to their limited value from a pharmacovigilance or clinical information perspective.

Specific Mapping Conventions

Principle 1. MedDRA LLT is mapped to SNOMED CT Fully Specified Name (FSN) concept, finding the same semantic match. The FSN is used to confirm the meaning. The same applies to the SNOMED CT concept to MedDRA LLT map.

Example

• MedDRA LLT Rhabdomyolysis maps to SNOMED CT Rhabdomyolysis (disorder)

• The map is not to SNOMED CT Rhabdomyolysis (morphologic abnormality) as this concept refers to a pathological related finding rather than a clinical one

• SNOMED CT Rhabdomyolysis (disorder) maps to LLT Rhabdomyolysis

Note that in this example, the starting LLT (Rhabdomyolysis) in the MedDRA to SNOMED CT map is the same as the LLT (Rhabdomyolysis) in the reverse SNOMED CT to MedDRA map. i.e., LLT 1 to FSN and FSN to LLT 1. 

Principle 2. When identifying maps, the synonyms in SNOMED CT are only used to inform the choice of the FSN. The maps do not allow mapping to synonyms.

Example

• MedDRA LLT Somnolence maps to SNOMED CT Drowsy (finding)
• SNOMED CT Somnolence is a synonym of Drowsy (finding) and cannot be used to map.
• Other LLTs under PT Somnolence such as LLT Sleepiness and LLT Sleepy are also included in the list of terms to map and these will also map to SNOMED CT Drowsy (finding), i.e., a many to one map. 

• In the reverse direction, SNOMED CT Drowsy (finding) maps to MedDRA LLT Drowsiness (1:1 map). “Drowsy” is not in MedDRA, only LLT Drowsy on awakening. MedDRA LLT Drowsiness is the closest match to SNOMED CT Drowsy (finding). 

Note that in this example, the source LLT (Somnolence) in the MedDRA to SNOMED CT map differs from the LLT (Drowsiness) in the reverse SNOMED CT to MedDRA map. i.e., LLT 1 to FSN (Drowsy) and FSN to LLT 2. This results from finding the closest match to SNOMED CT Drowsy which is LLT Drowsiness in MedDRA. All of the maps represent the same medical meaning however: LLT Somnolence and LLT Drowsiness both are under PT Somnolence and they are represented in SNOMED CT as FSN Drowsy (with its synonyms including Somnolence, Drowsiness, Sleepiness, etc.) 

Principle 3. Not Otherwise Specified (NOS) and Unspecified terms in MedDRA

• In the MedDRA to SNOMED CT map, NOS and unspecified LLTs are mapped to the unqualified SNOMED CT concept, i.e., without any further classification

  Example

  • LLT Pain NOS maps to SNOMED CT Pain (finding)

  • LLT Non-autoimmune hemolytic anemia, unspecified maps to SNOMED CT Non-autoimmune hemolytic anemia (disorder)

    
    

• NOS and unspecified concepts will not be added to SNOMED CT

• In the SNOMED CT to MedDRA map, the SNOMED CT FSN is mapped to the unqualified LLT, and will eschew mapping to NOS or unspecified LLTs in this direction

  Example

  • SNOMED CT Pain (finding) maps to LLT Pain

  • SNOMED CT Non-autoimmune hemolytic anemia (disorder) maps to LLT Non-autoimmune hemolytic anemia

Principle 4. UK English and US English variants

For MedDRA to SNOMED CT map:

• Both US and UK spelling variants in MedDRA are mapped to the SNOMED CT concept, i.e., the FSN which uses the US spelling. The UK spellings in SNOMED CT (descriptions) are synonyms and are used to help identify the correct FSN, but the actual map is to the FSN, not the synonym (see Principles 1 and 2).

Example

• • LLT Edema and LLT Oedema both map to SNOMED CT Edema (finding

• During the maintenance change request process, if a map is requested with a source LLT that exists in MedDRA using both the UK and US spellings (as in the oedema/edema example), the alternate spelling will also be added as an additional map with both LLTs mapping to the equivalent SNOMED FSN, which would use the US spelling as detailed above.

For SNOMED CT to MedDRA map:

Example

• • FSN Edema (finding) maps to LLT Edema (1:1 cardinality)

Note that clinical records using SNOMED CT use either UK or US spellings. When SNOMED CT is implemented in EHRs, a language subset (UK or US English) will be implemented by the system depending on the country of location. The end user will thus view the US or UK synonyms but these are represented by the unambiguous SNOMED CT concept which uses the US spelling.

Every PT in MedDRA has an LLT that is identical to it and shares the same code. In MedDRA, UK English spelling is used at the PT level and above; US spellings are only represented at the LLT level. Analysis is performed at the PT level. 

In the use case of taking SNOMED CT EHR data and converting it to MedDRA to report or count adverse events, one needs to avoid double counting. The 1:1 cardinality from SNOMED CT (US spelling) to MedDRA (US spelling) would ensure that events are only counted once in MedDRA. Maps are generated based on SNOMED CT concepts; whether the EHR uses the SNOMED CT US spelling or the UK spelling, both would map via the FSN to the same single term in MedDRA.

Principle 5. Combination terms and infection/body site

• MedDRA LLT is mapped to an equivalent SNOMED CT combination term if available

Examples

• • LLT Dementia due to Parkinson’s disease maps to SNOMED CT Dementia due to Parkinson’s disease (disorder)
  • LLT Escherichia urinary tract infection maps to SNOMED CT Urinary tract infection caused by Escherichia coli (disorder)

• Similar principles apply in the SNOMED CT to MedDRA map
• If an equivalent combination term is not available in either terminology, the term is flagged as unmappable for discussion and potential addition 

Principle 6. Test results

• MedDRA test result concepts are typically found in SNOMED CT (finding) but may also be represented in SNOMED CT (disorder)

Examples

• • MedDRA LLT Blood glucose increased maps to SNOMED CT Glucose in blood specimen above reference range (finding)

  • LLT Gastric acid increased maps to SNOMED CT Hyperchlorhydria (disorder)

Principle 7. Specimen type

• If the specimen type is not specified in the source concept/term, it is mapped to the concept/term without the specimen type, if available

• If the specimen type is not specified in the source concept/term and the concept/term without the specimen type is not available in the target terminology, it is acceptable to default to blood or the most common specimen type for that particular test

• The default specimen type is serum, not plasma, if blood is specified.

• The maps attempt to preserve the specimen type whenever possible.

Examples

• • LLT Drug level increased maps to SNOMED CT Blood substance level above reference range (finding) [there is no drug level high concept without the specimen type available so it is acceptable to default to blood]
  • LLT Lactate dehydrogenase increased maps to SNOMED CT Serum lactate dehydrogenase level above reference range (finding) [concepts for the increased/elevated term without the specimen type, or specifying blood or plasma are not available so it is acceptable to map to serum in this case]
  • LLT Blood creatinine increased maps to SNOMED CT Serum creatinine above reference range (finding)

Principle 8. Tumour types and stages

• SNOMED CT accepts tumor concepts included in the International Classification of Diseases for Oncology (ICD-O). A topography code and a morphology code express the complete morphological assessment as stated by the pathologist.

• MedDRA contains staging and classification systems that are used in clinical research and pharmacovigilance

• If one terminology does not contain a term with both the histopathologic type and site of the tumour, the term is flagged as unmappable and reviewed for possible addition. (Renal granular cell carcinoma is an example of a concept/term combining both the histopathologic type and tumour site and it is contained within both terminologies)
• When a term specifies histopathologic type, tumour site, and staging, efforts are made to preserve all three aspects of the concept in the maps. Staging information is not always represented in SNOMED CT, however. In these cases, the term is mapped to the primary cancer

Example

• • LLT Non-small cell lung cancer stage IIIB maps to FSN Non-small cell carcinoma of lung, TNM stage 3 (disorder)

• When a “recurrent” cancer term is not available in either terminology, the term is mapped to the primary cancer

Example

• • LLT Non-small cell lung cancer recurrent maps to FSN Non-small cell lung cancer (disorder)

• Metastatic primary site terms are synonymous with stage IV/stage 4 if the metastatic term is not available

Example:

• • LLT Lung adenocarcinoma metastatic maps to FSN Adenocarcinoma of lung, stage IV (disorder)

• For metastatic or stage 4 cancers, when an exact match is not available, “[Primary site] metastatic cancer” or “[Primary site] stage 4/stage IV cancer” LLTs map to the similar FSNs “Primary malignant neoplasm of [primary site]

Example:

• • LLT Lung cancer metastatic maps to FSN Primary malignant neoplasm of lung (disorder)

• Close attention is given to “secondary malignant neoplasm” and “metastases to” concepts. “Secondary malignant neoplasm of [organ]” and “Metastases to [organ]” LLTs map to FSNs of “Metastatic malignant neoplasm to [organ]”

Example:

• • LLT Metastases to spine maps to FSN Metastatic malignant neoplasm to vertebral column (disorder)

Principle 9. Increased/high and decreased/low qualifiers

• In both MedDRA and SNOMED CT, qualifiers for investigation results such as increased/high/elevated and decreased/low are generally used synonymously and can be used to map in both directions.
• In both terminologies, “increased” and “decreased” are generally used by reporters to refer to changes above and below the normal reference ranges (see example below for how this is sometimes reflected in the SNOMED CT hierarchy). 

Example

• LLT Bilirubin elevated maps to SNOMED CT Bilirubin level above reference range (finding). 

Additional Information

Contact mapping@meddra.org or info@snomed.org for additional information or inquiries regarding request for change criteria.