The 27 System Organ Classes (SOCs) represent parallel axes that are not mutually exclusive. This characteristic, called “multiaxiality,” allows a term to be represented in more than one SOC and to be grouped by different classifications (e.g., by aetiology or manifestation site), allowing retrieval and presentation via different data sets. Grouping terms are pre-defined in MedDRA and not selected on an ad hoc basis by data entry staff. Rather, the terminology is structured so that selection of a data entry term leads to automatic assignment of grouping terms higher in the hierarchy. Multiaxial links of terms are pre-assigned (and should not be changed), ensuring comprehensive and consistent data retrieval, irrespective of which SOC is selected at data retrieval.
Each MedDRA Preferred Term is assigned a primary hierarchy and, in some cases, secondary hierarchies. MedDRA users can produce a safety report with frequency counts using the primary SOC to highlight the distribution of adverse events in a data set. Using the primary SOC allocation will ensure that each event is only counted once for the report. It is also instructive to produce reports using the secondary SOC allocations to provide a more comprehensive view of the data. These features provide the user with great flexibility in accessing, displaying, and analysing MedDRA-coded data.
For example, the PT Influenza represents an important respiratory tract problem as well as an infection. For this reason, each PT is assigned to a primary SOC, but may also be assigned to one or more secondary SOCs. The PT Influenza is primary to the SOC Infections and infestations, but this PT is also secondary to the SOC Respiratory, thoracic and mediastinal disorders.