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Background: Developments in outcome measures in the rheumatic diseases are promoted by the development of successful treatments. Giant cell arteritis (GCA) is a multifaceted disorder and, therefore, measurement of multiple outcomes is relevant to this illness. It is a privilege to analyze and monitor/transfer long-term patients' management outcomes particularly if the same outcomes are used in practice and in trials., Objective: To classify the outcome measures for GCA with a discriminative ability to identify the disease activity status and response to therapy., Methods: This study was composed of two steps, instrument design (item generation) and judgmental evidence. A panel of 13 experts was used to validate the instrument through quantitative (content validity) and qualitative (cognitive interviewing) methods. Content validity index was used to assess content validity quantitatively., Results: Five items achieved high content validity where item-content validity index score was >0.79, and in the meantime achieved high content validity response score reflecting greater agreement among panel members. Through qualitative methods, items were improved until saturation was achieved. This agreed with the expert panel ranking of the items included in GCA disease outcome measures set., Conclusion: For daily clinical practice, outcome measures should reflect the patients' disease activity status and have to be easily assessed and recorded. The study identified composite outcome measures for GCA able to assess the disease state and monitor response to therapy. Key Points • Despite the cohort studies published in giant cell arteritis (GCA), there are no fully validated outcome measures for use in standard practice or clinical trials. • There is a gap in international standards for assessing GCA disease activity. • Identifying disease specific outcome measures is vital for monitoring response to therapy, treatment case series and therapeutic clinical trials in GCA. • This study was carried out aiming to classify the outcome measures for GCA with a discriminative ability to identify the disease activity status and response to therapy., (© 2023. The Author(s), under exclusive licence to International League of Associations for Rheumatology (ILAR).)