A Core Outcome Measurement Set (COMS) for Research and Clinical Practice in Post COVID-19 Condition (Long COVID) in Adults: An International Delphi Consensus Study

Background: Agreement is lacking regarding which instruments should be used for measurement of a recently-agreed core outcome set (COS) for clinical practice and research in post COVID-19 condition, also known as Long COVID. Methods: A rigorous multi-step consensus study was conducted, including a comprehensive literature review informing a three-round online modified Delphi process followed by an online consensus meeting to finalise measurement instruments for this COS, thereby developing a Core Outcome Measurement Set (COMS). 594 participants from 58 countries spanning six continents, participated in the consensus process. Findings: Consensus was reached for including the ‘modified MRC Dyspnea Scale’ for measuring the ‘Respiratory functioning, symptoms, and conditions’ outcome in the COMS. Two outcome measures from the acute COVID-19 COMS were included in this post COVID-19 conditionCOMS, namely ‘Time until death’ (for the Survival outcome) and ‘Recovery Scale for COVID-19’ (for the Recovery outcome). Consensus, based on predefined criteria, was not reached for the other 9 outcomes of the COS. However, based on the study results, suggested measurement instruments are provided for ‘Fatigue’, ‘Post-exertion symptoms’; ‘Pain’, ‘Physical function’, ‘Work/occupational and study changes’ and for ‘Cardiovascular’, ‘Nervous system’, ‘Cognition’ and ‘Mental’ functioning, symptoms and conditions. Interpetation: This international COMS provides a framework for assessing post COVID-19 condition in global clinical research and practice settings. Further evaluation is warranted as new data emerges on the performance of measurement instruments for the COS for this new clinical condition.