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Medical Coding: need and solution MedDRA

Nomenclature for diseases, signs, symptoms, adverse events is as diverse as there are languages and cultures. However, in this fast globalising world, there is often a need for information to be shared between two entities, repeatedly, consistently. These different terms make it very challenging to measure, compare, communicate. There certainly a need for standardisation.

  • Across regulatory agencies
  • Across multinational pharmaceutical companies
  • For electronic data transfer
  • To avoids translation distortions/errors across countries

Standardisation was attempted by creation of a set of codes or dictionaried like

  • Coding symbols for a Thesaurus of Adverse Reaction terms (COSTART)
  • World Health Organization - Adverse Reaction Terminology (WHO – ART),
  • Hoechest Adverse Reaction Terminology (HART),
  • Japanese Adverse Reaction Terminology (J-ART),
  • ICD-9 ( International Classification of Diseases)

The limitation with these was

  • Lack specificity
  • Having limited data retrieval options
  • Inability to handle complex combinations of signs and symptoms (syndromes)

This was the case till the development of MedDRA (Medical Dictionary for Regulatory Activities).

MedDRA was developed under ICH, and is continuously enhanced to meet the evolving needs of its users

  • ICH created a governance structure to nurture and protect the integrity of MedDRA
  • MedDRA is maintained by Maintenance and Support Services Organization (MSSO) and is overseen by an ICH MedDRA Management Board appointed by the ICH Steering Committee that has overall responsibility for the direction of MedDRA, and oversees all the activities of the MedDRA Maintenance and Support Services Organization
  • Updates are released twice a year-in March and September
  • The terminology is used throughout the regulatory process, from clinical studies to post-marketing

Scope of MedDRA

With the help of MedDRA terminology, one can code diseases, surgical procedures, indications, adverse reactions, symptoms, signs, diagnoses and investigations. Thus, besides coding of reports adverse events/ reactions, signs and symptoms, MedDRA terminology can also be used for coding of social, family and medical history, therapeutic indications of suspect and concomitant drugs, provisional and confirmatory diagnoses, effects of rechallenge, investigational reports and cause of death.

However, MedDRA is:

  • Not a drug dictionary
  • Not a product dictionary
  • Patient demographics terms cannot be coded

Although MedDRA terminology is used for coding of medical information during all phases of clinical development and marketing, there is no frequency qualifier, no severity descriptor in the system.

Purpose of using MedDRA as accepted worldwide by now is

  • To aggregate reported terms in medically meaningful groupings for the purpose of reviewing and /or analyzing safety data.
  • To facilitate consistent retrieval of specific cases or medical conditions from a database.
  • To improve consistency in comparing and understanding “safety signals” and aggregated clinical data.
  • To report adverse reaction/adverse event (ADR/AE) terms via individual case safety reports.
  • To include ADR/AE’s in tables, analyses, and line listings for report.
  • To identify frequency of medically similar ADR/AEs.
  • To capture and present product indications, investigations, medical history and social history data.

Structure of MedDRA

MedDRA is a large terminology with a pyramid like structure. Terms in MedDRA are organized in 5 levels in a hierarchical manner viz. Low Level Terms (LLT); Preferred Terms (PT); High Level Terms (HLT); High Level Group Terms (HLGT) and System Organ Class (SOCs).

  • SOC (System Organ Class) - Highest level of the terminology, and distinguished by anatomical or physiological system, aetiology, or purpose
  • HLGT (High-Level Group Terms) – Subordinate to SOC, superordinate descriptor for one or more HLTs
  • HLT (High-Level Terms) – Subordinate to HLGT, superordinate descriptor for one or more PTs (links PTs related to it by anatomy, pathology, physiology, aetiology or function)
  • PT (Preferred Term) – Represents a single medical concept. PT can be connected to a single SOC (Single Axiality) or to SOC through multiple branches (Multiaxiality)
  • LLT (Lower-Level term) – Lowest level of the terminology. The LLT is the term that most accurately reflects the reporter’s words. There is 1:1 correspondence between LLT and Verbatim Terms

The use of MedDRA will be the topic of another article


  1. Introductory Guide MedDRA Version 24.1 September 2021
  2. MedDRA® TERM SELECTION: POINTS TO CONSIDER ICH-Endorsed Guide for MedDRA Users, Version 24.1March 2021
  3. Babre D,Medical Coding in Clinical Trials, PICR 2010;1:29
Dr. Vishwas Sovani (January 2022)


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MedDRA, WHODRA, HART, J-ART, scope, structure, Low Level Terms (LLT); Preferred Terms (PT); High Level Terms (HLT); High Level Group Terms (HLGT) and System Organ Class (SOCs).