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Question 8 of 20 Fundamentals Concept

What is medical coding, and why are MedDRA and WHODrug used?

Short answer

Medical coding maps the free text that sites write, such as 'tummy ache' or a brand name, to a standard dictionary term so events and medications can be counted and compared. MedDRA codes adverse events and medical history, and WHODrug codes medications.

Why

Without coding, 'headache', 'head pain' and 'cephalalgia' would be counted as three different events. MedDRA has five levels. Lowest level terms (LLTs) capture how people write, each LLT links to one preferred term (PT), and PTs roll up through high level terms and high level group terms into 27 system organ classes (SOCs).

MedDRA is multiaxial, so a PT can sit in more than one SOC, but each PT has one primary SOC used for counting so events are not double counted. New versions come out in March and September, for example 29.0 in March 2026 and 29.1 in September 2026, and a study fixes its version and plans how to handle upgrades. WHODrug Global, maintained by the Uppsala Monitoring Centre, codes concomitant medications, links trade names to substances and assigns Anatomical Therapeutic Chemical (ATC) classes, so medications can be analyzed by drug class.

It is released on 1 March and 1 September, and UMC notes FDA has mandated it for studies starting after 15 March 2019. Coders choose terms and do not reinterpret what the investigator meant. If the verbatim term is ambiguous, such as 'cold', the right step is a query to the site, not a guess between the common cold and feeling cold.

A strong answer covers

  • Purpose: consistent counting and comparison
  • MedDRA five level hierarchy and 27 SOCs
  • Primary SOC prevents double counting
  • Version control across a study
  • Query ambiguous verbatim terms rather than guess

Common mistakes

  • Changing the meaning of a verbatim term to make it easier to code.
  • Upgrading the MedDRA version mid-study without assessing the impact on coded terms.
  • Confusing WHODrug ATC classes with MedDRA system organ classes.