How should I plan a multi-registry search so I do not miss trials for a condition?

Plan the search in two layers: start with a portal that covers participating registries, then run condition- and status-specific searches in individual registries, and record each source and search date so the combined list can be deduplicated. The WHO ICTRP Search Portal provides a single access point for records supplied by participating clinical-trial registries, which makes it a practical first layer for reaching multiple registries at once. Because participation varies by registry, treat the portal result as a starting set and confirm coverage against the registries relevant to your condition.

1. Define the condition and eligibility terms before searching. Write the condition synonyms, intervention terms, and the trial statuses you will include, then use the same terms across sources so differences in results reflect the sources rather than the wording. The Cochrane Handbook describes planning searches and developing search strategies as explicit review steps.
2. Search the multi-registry portal first. Run the condition search in the WHO ICTRP Search Portal and save the result set with the date. This gives you a broad base drawn from participating registries.
3. Search individual registries by condition and status. ClinicalTrials.gov lets users search registered studies and filter records by condition, intervention, location, status, study type, dates, and other study fields. Apply the status filters you defined in step 1 and save each result set with its date.
4. Record every source and search date. Keep a log listing each portal or registry, the exact terms and filters used, the date, and the number of records returned. The Cochrane Handbook describes documenting searches and managing records as part of the review process.
5. Deduplicate the combined list. Merge the saved sets and match records on registry identifier, title, and condition to remove duplicates, keeping the source where each unique trial was found. The output is a deduplicated trial list with a documented trail of which portal or registry supplied each record.
6. Check reference lists and other sources for trials the registry searches did not return. The Cochrane Handbook describes searching reference lists and other sources alongside database searches.

Use the documented log to show which registries were covered and which searches produced each trial, so the final list can be re-run or extended later.