How should trial and systematic review registrations be cited?

Overview

Trial registrations are for randomized controlled trials (RCTs) and randomized trials (RTs), protocols for RCTs and RTs, if available, and sometimes related papers, like substudies or parallel studies of RCTs and RTs. For more information, see the articles below:

• Does my trial (RCT) have to be registered?
• I'm publishing a paper about a randomized controlled trial. What specific items are required for publication?

Trial registrations should be added to the article's metadata page as part of the abstract using the "Trial Registration" field. They can also be mentioned in the body of the manuscript itself (ie, Methods section). Trial registrations should not be added to the reference list unless the database itself is being studied.

The Trial Registration section of the abstract is also used to present review registrations.

How should trial registrations and systematic review registrations be formatted?

On the metadata page (in the Trial Registration section of the abstract), trial registrations should be formatted as follows:

[Name of database] [Trial number]; [Database URL]

Common clinical trial databases include:

• Australian New Zealand Clinical Trials Registry (Australia & New Zealand)
• Netherlands Trial Register (Netherlands)
• ISRCTN Registry (United Kingdom)
• ClinicalTrials.gov (United States)
• Chinese Clinical Trial Registry (China)
• German Clinical Trials Register (Germany)

Common systematic review databases include:

• PROSPERO (International)
• Cochrane Database of Systematic Reviews (International)
• OSF Registries (International)

The full list of WHO data providers and WHO primary registries can be found at:

• https://www.who.int/clinical-trials-registry-platform/network/data-providers
• https://www.who.int/clinical-trials-registry-platform/network/primary-registries 
• https://www.who.int/clinical-trials-registry-platform/network/partner-registries

Examples:

• ClinicalTrials.gov NCT12345678; https://clinicaltrials.gov/ct2/show/NCT12345678
• ISRCTN Registry ISRCTN12345678; http://www.isrctn.com/ISRCTN12345678
• Netherlands Trial Register NL1234; https://www.trialregister.nl/trial/1234
• Australian New Zealand Clinical Trials Registry ACTRN12345678912345; https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=654321
• PROSPERO CRD42019123456; https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=123456
• OSF Registries osf.io/y4bhs; https://osf.io/y4bhs 
  • Be sure that the link provided leads to a page labeled as "OSF Registries" and not "OSF Home"

Multiple trial registrations

• If there are multiple trial registrations for a paper, avoid using any punctuation after the URL as they will be automatically included in the URL and cause it to open to an invalid webpage. Instead, use the word “and” to separate them:
  • 2 registrations, same registry:
    • ClinicalTrials.gov NCT12345678; https://clinicaltrials.gov/ct2/show/NCT12345678 and NCT87654321; https://clinicaltrials.gov/ct2/show/NCT8765432
  • 2 registrations, different registries:
    • ClinicalTrials.gov NCT12345678; https://clinicaltrials.gov/ct2/show/NCT12345678 and ISRCTN Registry ISRCTN12345678; http://www.isrctn.com/ISRCTN12345678