Standards
ClinicalTrials.gov identifier (NCT number)
A stable identifier for a clinical study record on ClinicalTrials.gov.
- Kind
- Identifiers
- Steward
- ClinicalTrials.gov, U.S. National Library of Medicine
- Official source
- https://clinicaltrials.gov/
What it describes
An NCT number identifies a clinical study record registered on ClinicalTrials.gov. It is a reliable locator for the public record and its posted history. It does not itself identify a protocol version, a trial site, an intervention, or a publication. A study can acquire updates to status, outcomes, and administrative details while retaining the same NCT identifier.
When a claim depends on what a registry displayed at a particular time, cite the record and the relevant posted version or retrieval date. Registration is not evidence that results are complete, that an intervention is effective, or that all study conduct matched the plan. Distinct related studies can have separate NCT records, so names and sponsors should not be used as the sole matching keys.
Structure
The prefix NCT followed by eight digits.
Useful for
- Locate a study's registry history.
- Join publications to registered studies.
- Distinguish similarly titled trials.
Limits
- Does not encode phase or outcome.
- Registry fields can change over time.
- Registration does not establish efficacy.
How it is used in practice
Registering a trial on ClinicalTrials.gov produces an NCT number, and that number then follows the study through publications, regulatory submissions and press releases. Medical journals following the International Committee of Medical Journal Editors recommendations expect trials to be registered before enrolment and to give the registration identifier in the paper. Analysts use the NCT number to join a publication to its registry entry, to compare what was planned with what was reported, and to find all studies of a drug or condition.
The record behind the number is not static. Sponsors update recruitment status, enrolment, outcome measures and results over the life of a study, and the site keeps a history of changes. The number identifies the study record across all of those versions, which is the reason the version or retrieval date must accompany any claim that depends on what the record said.
A worked example
A fictional sponsor, Halden Therapeutics AG, announces positive results for a phase 2 study of a fictional compound and gives its NCT number. A reviewer wants to know whether the primary outcome reported in the announcement is the one registered before the study started.
The reviewer opens the registry record and its history of changes. The earliest version lists one primary outcome; a later version, posted before results, lists another. The announcement reports the later one. The reviewer records this as an observation with both version dates and the passages of each, without drawing a conclusion about intent: the primary outcome in the announcement differs from the outcome in the earliest registered version, and the registry shows when it was changed. Whether the change was appropriate is a separate question that requires the protocol and statistical analysis plan.
Evaluating a claim that rests on an NCT number
The claim should say which version of the record it relies on. A status of recruiting, completed or terminated is a field with a date. Results sections are posted on different schedules, and the absence of results can mean that none are due, that they are delayed, or that the study never completed. The registry gives data and dates and rarely gives reasons, so a reason has to come from another document.
Link publications by NCT number rather than by title, and check the match in both directions: the publication should cite the NCT number, and the registry record may list the publication. One study may have several publications, and a publication may report several studies. If a drug is the subject of a claim, the intervention fields identify it by name as entered by the sponsor, and a name-to-substance link should be made through a substance identifier with its own source.
Confusions to avoid
An NCT number is not an approval, an endorsement or a quality mark. Registration is a disclosure step. It does not mean the study was reviewed for design quality by the registry, and a registered study may be small, terminated early or never reported.
It is also not the only registry identifier a study may carry. Studies are frequently registered in more than one registry, including those participating in the World Health Organization's international platform, and may carry sponsor protocol numbers and regulatory identifiers. Records that merge these should show each identifier with its source and note that the links among them come from the registry fields or from the sponsor, not from an assumption that similar titles imply the same study.
Questions a reviewer can ask
Which version of the registry record was read, and what does its history show? Does the publication cite the NCT number, and does the record cite the publication? Are the primary outcomes, enrolment and status in the claim the registered values or later changes? Were results posted, and are they due? Does the record link to other registrations of the same study? What does the claim assume about the intervention, and which field supports it?
Related terms
Found an error on this page? See corrections for what counts as one, how to report it and the dated log.
Enquiry
Which of your sources carry ClinicalTrials.gov identifier (NCT number)?
Tell us which sources carry it, which key the same entity some other way and who may read which. We reply with whether and how a first record would use this identifier.
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