Abstract / Summary
ABSTRACT Introduction Psychiatric biomarker research has traditionally been organized around diagnostic categories, but clinical heterogeneity, comorbidity and shared biological mechanisms across psychiatric conditions have increased interest in transdiagnostic approaches. These approaches may be especially relevant for early recognition, stratification and intervention planning. Despite this growing interest, the concept of the transdiagnostic biomarker remains unclear. This conceptual review aimed to clarify how transdiagnostic biomarkers of psychopathology are represented in psychiatric research. Methods Systematically identified empirical literature and concept explication were used to examine biomarker modalities, indexed psychopathology‐related constructs, transdiagnostic framing and conceptual boundary issues across studies. Results Transdiagnostic biomarker research was found to encompass several approaches, including diagnosis‐spanning comparisons, symptom‐based models, subgroup‐based approaches, cross‐domain extensions beyond traditional psychiatric categories and research aligned with alternative frameworks such as the Research Domain Criteria or the Hierarchical Taxonomy of Psychopathology. A conceptual framework is proposed comprising three linked elements: the measurable indicator, the psychopathology‐related construct and the transdiagnostic scope of that construct. Within this framework, a transdiagnostic biomarker is defined as a measurable biological or biobehavioural indicator of a psychopathology‐related construct that spans multiple diagnostic categories or extends beyond them. Conclusion Greater conceptual clarity of transdiagnostic biomarkers may strengthen psychiatric biomarker discovery by improving construct alignment and supporting their use in biomarker‐informed stratification, early intervention, treatment selection, prognosis and precision psychiatry.