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Randomised clinical trial (RCT)
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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.

C

CDASH (Clinical Data Acquisition Standards Harmonization)

Clinical Data Acquisition Standards Harmonization (CDASH) is a CDISC standard for collecting clinical research data consistently across studies and sponsors. It helps teams design collection fields and questions with traceability to later tabulation. CDASH concerns acquisition, while SDTM concerns how study data are organised for tabulation and review.

Key takeaways

  • CDASH standardises data acquisition, while SDTM standardises tabulation; the two stages connect but do not represent identical data structures.
  • CDASH supports consistent questions, field definitions and terminology, helping teams document how collected information becomes data used for regulatory review.
  • A standard collection field is not automatically necessary for every protocol, so study teams should still justify what they collect.

From Collection to Submission

StageRole
eCRF designImplement study-specific questions and fields
CDASHProvide consistent acquisition conventions
SDTM mappingOrganise collected data for tabulation

CDISC’s CDASH guidance describes traceability between collection and SDTM. Some collected variables map directly; others require transformation. Do not assume that using similar variable names removes the need to specify and test those mappings.

For example, consider a hypothetical study recording medication duration. A collection form might capture a value and unit separately, while a tabulated variable uses a standard duration representation. Documenting that transformation helps reviewers understand the relationship without guessing what the site entered.

Why It Matters for Data Protection

Operationally, use CDASH as a starting point for consistent design, then check each field against the protocol and its intended purpose. Review direct identifiers and free text particularly carefully, because a standardised database can still collect unnecessary or revealing information.

We recommend involving data management, clinical operations and privacy reviewers before database build. Record which fields are required, who can view them and what is included in exports to the sponsor or external analysts. This is easier to resolve before collection than after data have been distributed.

Frequently Asked Questions

Is CDASH an electronic data capture platform?

No. It is a standard that can inform the design of forms implemented in a platform.

Does CDASH replace SDTM?

No. Acquisition and tabulation are complementary stages.

Must every possible standard field be collected?

No. The study’s purpose and applicable requirements determine the necessary data.

Related: electronic case report forms; SDTM; clinical-trial privacy support.

Updated: 27 October 2026