What are the five levels of the MedDRA dictionary?

The MedDRA dictionary hierarchy is a categorization of medical terminology. The five levels of the dictionary are System Organ Class (SOC), High Level Group Term (HLGT), High Level Term (HLT), Preferred Term (PT), and Lowest Level Term (LLT).

The lower the level of the dictionary, the more precise the medical terminology becomes. Preferred Terms (PTs) represent medical terms you can use as the end result for coding.

For the example:

If the term to code is "queasy," the preferred equivalent medical term (PT) is "Nausea" in the context of the following hierarchy:
System Organ Class (SOC) = Gastrointestinal disorders
High Level Group Term (HLGT) = Gastrointestinal signs and symptoms
High Level Term (HLT) = Nausea and vomiting symptoms
Preferred Term (PT) = Nausea
Lowest Level Term (LLT) = Feeling queasy