Methods for developing diagnostic criteria for conditions without objective tests, biomarkers or reference standards: a scoping review

When lab tests or scans aren't available to confirm a diagnosis, doctors may use diagnostic criteria to help them decide what condition a patient may have. There is currently no clear way to create these criteria, which can lead to inconsistency and confusion. We looked at why this matters - because diagnostic criteria developed without transparency or methodological rigour may lead to incorrect diagnosis, patient harm or inequitable access to care - and explored how researchers develop diagnostic criteria when an objective test doesn't exist. Most studies relied on expert meetings, but many did not explain how they chose experts, gathered evidence or involved diverse perspectives such as patient voices. Our research shows that current practices often aren't well explained and may be biased or incomplete. By understanding what's missing and what may work, we hope this study encourages better, more transparent methods so that future diagnostic criteria are clearer, fairer and more trustworthy for both patients and healthcare providers.