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Term of the Day

Natural history study

A natural history study is a preplanned observational study intended to track the course of a disease over time, identifying demographic, genetic, environmental and other variables that correlate with its development and outcomes in the absence of intervention, or under standard of care. Designs may be retrospective (chart review of existing records) or prospective (longitudinal follow-up of a cohort or registry).

Natural history data is particularly important in rare and paediatric diseases, where randomised placebo-controlled trials may be infeasible or unethical. The FDA (guidance on rare disease natural history studies, 2019) and the EMA accept well-designed natural history studies to define endpoints and biomarkers, identify patient subgroups, estimate sample sizes and, in some cases, serve as external or historical control arms for single-arm trials supporting orphan products.

Because they are non-interventional, natural history studies fall outside the CTR and are governed by national law (for example France's MR-003 or MR-004 reference methodologies) and by the GDPR. They typically involve secondary use of medical records, long-term follow-up, genetic data and small populations in which anonymisation is rarely achievable, so pseudonymisation, a DPIA and a robust research legal basis under Art. 9(2)(j) are essential. Registries maintained by patient organisations or academic consortia raise additional questions of joint controllership and data access governance.

M

MedDRA

MedDRA, the Medical Dictionary for Regulatory Activities, is a standardised medical terminology used to classify and communicate medical information in regulatory activities. It supports consistent coding and analysis, including adverse events in clinical trials and pharmacovigilance. Its hierarchical terms organise concepts; using them does not, by itself, anonymise a patient record.

Key takeaways

  • MedDRA provides a structured terminology for medical information.
  • Its hierarchy runs from broad classes to specific terms.
  • A coded event can still belong to an identifiable person.

How the Five-Level Hierarchy Works

The MedDRA introductory guide explains the hierarchy and relationships between terms. Lowest Level Terms support precise coding, while Preferred Terms and broader groupings help organise retrieval and analysis. MedDRA is multiaxial: a concept may be represented through more than one relevant System Organ Class. The hierarchy should not be mistaken for a simple severity scale.

LevelFull name
SOCSystem Organ Class
HLGTHigh Level Group Term
HLTHigh Level Term
PTPreferred Term
LLTLowest Level Term

Why It Matters for Data Protection

As an operational recommendation, treat the original event description, coded term and associated participant information as separate review points. The EDPB distinguishes pseudonymisation from anonymisation. Free text may contain identifiers that a dictionary code does not remove. Restrict access to the underlying narrative, preserve necessary clinical meaning and document the terminology version used so reviewers can understand the coding context.

Hypothetical example: A clinical data team receives an adverse-event narrative containing a participant’s occupation and a named hospital. It recommends reviewing unnecessary identifying details before broader circulation, then selecting an appropriate MedDRA term without inventing a diagnosis. The source record and coding decision remain traceable for authorised review.

Frequently Asked Questions

Is a MedDRA code a diagnosis?

Not necessarily. The terminology also includes symptoms and other medical concepts; coding should reflect the reported information.

Does coding establish that a drug caused the event?

No. Classification and causality assessment are different tasks.

Does MedDRA remove data protection obligations?

No. A terminology code does not establish that the surrounding record is anonymous.

Related reading: adverse event, pharmacovigilance.

For practical implementation, explore clinical research support.

Updated: 27 October 2026