The organization of MedDRA is one of its most unique features. It’s structured in a hierarchical manner, which means it’s organized from very specific to very general. This structure is what makes MedDRA so flexible and precise.
Imagine MedDRA as a tree. At the top of the tree, you have the most general terms, and as you move down the tree, the terms become more specific. This tree-like structure is known as the MedDRA hierarchy.
The MedDRA hierarchy consists of five levels: System Organ Class (SOC), High-Level Group Term (HLGT), High-Level Term (HLT), Preferred Term (PT), and Lowest Level Term (LLT). Each level represents a different degree of specificity.
Let’s take a closer look at each level:
- System Organ Class (SOC): This is the highest level of the hierarchy. SOCs are based on etiology, manifestation site, or purpose. For example, “Cardiac disorders” is an SOC.
- High-Level Group Term (HLGT): HLGTs are subcategories within an SOC. They provide a more specific classification. For example, “Cardiac arrhythmias” is an HLGT under the SOC “Cardiac disorders”.
- High-Level Term (HLT): HLTs are even more specific than HLGTs. They represent distinct clinical concepts. For example, “Ventricular arrhythmias” is an HLT under the HLGT “Cardiac arrhythmias”.
- Preferred Term (PT): PTs are single medical concepts. They are used for data entry and retrieval. For example, “Ventricular fibrillation” is a PT under the HLT “Ventricular arrhythmias”.
- Lowest Level Term (LLT): LLTs are the most specific level of the hierarchy. They represent specific medical conditions or symptoms. For example, “Acute ventricular fibrillation” is an LLT under the PT “Ventricular fibrillation”.
This hierarchical structure allows for flexibility and precision in coding and reporting. It ensures that every medical term has its place in the hierarchy, making it easy to find and categorize.