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 

A major goal of the WEB-RADR 2 project is 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 are also included in the first production release of the maps to capture important aspects of the pandemic.

In one use case, these key pharmacovigilance concepts when coded in SNOMED CT in an electronic health record (EHR) could be converted to MedDRA for the purpose of adverse event reporting to regulatory authorities or for the purposes of epidemiological research. In the opposite direction, these same key terms coded in MedDRA representing adverse events, warnings, and other regulatory information could be converted into SNOMED CT so that the information is available in the patient’s record to aid in clinical decision-making.

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 (April-September 2020)

Final 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 

MedDRA hierarchies 

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 current as of January 2021 and are intended for illustrative purposes.

Determining possible equivalencies 

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

• 

Mapping to an exact conceptual match 

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 maps to LLT Cardiac pacemaker insertion

Example 2:

• • LLT Emotional lability maps to SNOMED CT Mood swings

  • SNOMED CT Mood swings 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.

Unmappable Concepts / Terms

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.

Source Terms

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/PT 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.

Map terms

Taking the MedDRA to SNOMED CT map as an example, in many instances, the LLT/PT 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 Blood pressure systolic maps to FSN Systolic arterial pressure (observable entity)

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. Map MedDRA LLT to SNOMED CT concept, finding the same semantic match.

Use Fully Specified Name (FSN) to confirm meaning. The same applies to the SNOMED CT concept to MedDRA LLT map.

Example

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

- Do not map 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, only use the synonyms in SNOMED CT to inform choice of the FSN. 

The tool will not permit 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, LLT Sleepy, and LLT Daytime sleepiness 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 maps to MedDRA LLT Drowsiness(1:1map) “Drowsy” is not in MedDRA, only LLT Drowsy on awakening. MedDRA LLT Drowsiness is closest match to SNOMED CT Drowsy. 

Note that in this example, the starting 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, map NOS and unspecified LLTs to the unqualified SNOMED CT concept, i.e., without any further classification

  Example

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

  • ›  LLT Non-auto immune hemolytic anemia, unspecified maps to SNOMED CT Non-auto immune 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, i.e., do not map to NOS or unspecified LLTs in this direction

  Example

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

  • ›  SNOMED CT Non-autoimmune hemolytic anemia maps to LLT Non-autoimmune hemolytic anemia

Principle 4. UK English and US English variants

For MedDRA to SNOMED CT map:

• »  Map both US and UK spelling variants in MedDRA to the SNOMED CT concept, i.e. the FSN (US and

  UK spellings (descriptions) are synonyms and can’t be used to map)

  Example

  › LLT Edema and LLT Oedema map to SNOMED CT Edema (cardinality of 1:1)

  
  

• »  If the MedDRA source data set contains only either the UK or US spelling of an LLT, the MSSO will

  identify and review the equivalent alternate missing spellings for possible addition to the mapping.

  Post-mapping note: in finalizing the mapping, all “missing” spelling variants in the MedDRA source data were identified and mapped to the appropriate FSN (US spelling). 

For SNOMED CT to MedDRA map:

Example

› FSNEdemawillmaptoLLTEdema(1:1cardinality) 

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 (AEs), 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

» Map MedDRA LLT 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

› LLT Escherichia urinary tract infection maps to SNOMED CT Escherichia coli urinary tract infection

» Similar principles apply in the reverse SNOMED CT to MedDRA direction
» If an equivalent combination term is not available in either terminology, flag as Unmappable for discussion and potential addition 

Principle 6. Test names and test results

» MedDRA test name term concepts will generally be found in (procedure) concepts in SNOMED CT

Examples

• MedDRA LLT Cholesterol maps to SNOMED CT Cholesterol measurement (procedure), not SNOMED CT Cholesterol (substance)
  
  

» MedDRA test results are typically found in SNOMED CT (finding)

Examples

• MedDRA LLT Blood glucose increased maps to SNOMED CT Increased glucose level (finding)

• SNOMED CT Increased glucose level maps to MedDRA LLT Glucose increased (SOC Investigations) 

MedDRA has important exceptions for the following high/low, increased/decreased terms which are considered to be disorders rather than investigations based on the common use of these terms:

› LLT Blood pressure high (PTHypertension)
› LLT Blood pressure low (PTHypotension)
› LLT High temperature (PTPyrexia)
› LLT/PT Sputum increased (HLT Coughing and associated symptoms)

› LLT/PT Sputum decreased (HLT Coughing and associated symptoms)

The corresponding SNOMED CT concepts will also therefore be disorders.

Examples

› LLT Blood pressure high maps to SNOMED CT Hypertensive disorder, systemic arterial (disorder)

› LLT Blood pressure low maps to SNOMED CT Low blood pressure (disorder)

Post-mapping note: although unqualified test name terms were included in the MedDRA source data, it proved challenging to map many of them to SNOMED CT. In addition, since these terms only convey that a test was performed, they were considered not to be of value from a pharmacovigilance or clinical information perspective. Therefore, unqualified test name terms were removed from the final mapping. 

Principle 7. Specimen type

• »  If the specimen type is not specified in the source concept/term, it should be 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 will be serum, not plasma, if blood is specified. Try to preserve the specimen type whenever possible.

  Examples

  • ›  LLT Lactate dehydrogenase maps to SNOMED CT Lactate dehydrogenase level (not to SNOMED CT Plasma lactate dehydrogenase level)

  • ›  LLT Drug level increased maps to SNOMED CT Blood drug level high (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 elevated (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 maps to SNOMED CT Creatinine measurement, serum 

Principle 8. Tumour types and stages

• »  If SNOMED CT does not contain an FSN with both the histopathologic type and site of the tumour, the MedDRA term should be flagged as “Unmappable in SNOMED CT” and reviewed for possible addition.

  Example

  › LLT Renal granular cell carcinoma does not have a corresponding FSN within SNOMED CT and should be marked Unmappable.

  
  

• »  SNOMED CT does not contain all stages for specific tumour types. If the tumour stage concept is not available in SNOMED CT for a particular stage term in MedDRA, the term should be flagged as “Unmappable in SNOMED CT” and reviewed for possible addition.

  Example

  › LLT Breast cancer stage III does not have a corresponding FSN within SNOMED CT and should be marked Unmappable.

  
  

• »  When a “recurrent” cancer term is not available in SNOMED CT then the term should be mapped to the primary cancer.

  Example

  › LLT Non-small cell lung cancer recurrent maps to FSN Non-small cell lung cancer 

  
  

• »  When a MedDRA term specifies cell type and site, in addition to staging, try to preserve all three aspects of the concept in the SNOMED CT map.

   Examples

   ›  LLT Lung adeno carcinoma metastatic maps to FSN Adeno carcinoma of lung, stage IV

   ›  LLT Adeno carcinoma of colon stage IV is unmappable due to the lack of atermin SNOMED CT that captures Adenocarcinoma + Colon + stage IV/4/metastatic, including the “metastatic from” form referenced below.

The exceptions to this principle are the stage 4 or metastatic cancers.

• »  For metastatic or stage 4 cancers, when an exact match is not available, “[Primary site] metastatic cancer” LLTs map to the similar “Metastasis from [primary site]” FSN

  Example

  › LLT Lung cancer metastatic maps to FSN Metastasis from malignant neoplasm of lung

  
  

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

  Example

  › LLT Lung adeno carcinoma metastatic maps to FSN Adeno carcinoma of lung, stage IV

  
  

• »  Close attention should be given to the “secondary from” and “metastatic to” terminology.“ Metastases [organ]” LLTs map to FSNs of “Secondary malignant neoplasm of [organ]”

  Example

  › LLT Metastases to spine maps to FSN Secondary malignant neoplasm of vertebral column 

Principle 9. Natural word order

» When mapping from SNOMED CT to MedDRA and there are several lexical variant LLTs, the one that uses natural word order should generally be chosen. However, because of the granularity of MedDRA, there may be several LLTs under a PT that are all equally acceptable. If the map specialists happen to choose different ones, the map lead will mark them as not in conflict and select one LLT as the mapped term.

Examples

• ›  SNOMED CT Hyperpigmentation of skin maps to LLT Skin hyperpigmentation (natural word order) rather than LLT Hyperpigmentation skin

• ›  SNOMED CT Collapse of vertebra could map to LLT Collapsed vertebra or LLT Vertebral collapse. Both use natural word order and are under PT Spinal compression fracture. 

Principle 10. Punctuation marks

SNOMED CT concepts typically do not include punctuation marks such as hyphens or slashes and will be mapped to the equivalent MedDRA term that also does not include these marks. If there is no MedDRA term without punctuation marks available, the SNOMED CT term will be mapped to the equivalent MedDRA term with punctuation marks. New terms without punctuation marks will be considered for potential addition to MedDRA.

Example

› ForSNOMEDCTAttentiondeficithyperactivitydisorderthereareonlypunctuatedLLTs:LLT Attention deficit/hyperactivity disorder and LLT Attention deficit-hyperactivity disorder

Principle 11. 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, the clinical meaning of the “increased” qualifiers can refer to an increase from a previous baseline or an increase above the normal range for that parameter. Similar considerations apply to concepts/terms that are “decreased”. Since it is not known from the report which clinical meaning applies unless one reviews the actual laboratory data, the qualified investigation terms in each terminology will be mapped to their equivalent counterparts. In practice, it is likely that “increased” and “decreased” are generally used by reporters to refer to changes above and below the normal reference ranges (see Increased bilirubin level example below for how this is sometimes reflected in the SNOMED CT hierarchy). However, for the purpose of this bi-directional mapping, the concepts/terms will be mapped strictly to their equivalents since the underlying clinical meaning is not known on an individual case basis.

Example

› LLT Bilirubin elevated maps to SNOMED CT Increased bilirubin level (finding). Note that the interpretation is “Above reference range”. 

Example

› LLT Blood pressure systolic increased maps to SNOMED CT Increased systolic arterial pressure (finding). Note that in this case the interpretation is “Increased” but it does not state if this is above the reference range.