Lesson 1 of 3 · about 15 min
How MedDRA is built
MedDRA is a hierarchy with five levels, from the most general to the most specific:
- System Organ Class (SOC): 27 body-system groupings, such as Cardiac disorders
- High Level Group Term (HLGT)
- High Level Term (HLT)
- Preferred Term (PT): one distinct medical concept. This is the level used for counting and reporting
- Lowest Level Term (LLT): the most specific level, including synonyms and spelling variants. This is the level you select
You code at LLT level. Each LLT links to one PT, so choosing the LLT chooses the PT. Always pick an LLT that is marked current. Non-current terms stay in the dictionary for old data, but you should not use them for new cases.
A PT can sit under more than one SOC, but only one is its primary SOC. Aggregate outputs usually sort by the primary SOC, which is why a PT can show up under an unexpected organ class in a table.
MedDRA is maintained by the MSSO under ICH and is updated twice a year, in March and September. Your organisation will state which version a given database is on. Mixing versions inside one analysis is a common cause of mismatched counts.