The Glucocorticoid Toxicity Index (GTI) is a composite instrument designed to capture change in glucocorticoid-related morbidity over time.1 It was developed through consensus methods and multi-criteria decisions among 19 medical specialists, with relative domain weights decided via clinician consensus.2 The GTI has now been used in more than 45 studies, including 12 phase 3 clinical trials.1The GTI comprises eight domains: body mass index, blood pressure, glucose tolerance, lipid metabolism, glucocorticoid myopathy, skin toxicity, neuropsychiatric effects and infections. Two overall scores are calculated: the cumulative worsening score (CWS), which includes transient and permanent GC toxicity from baseline to specific time points, and the Aggregate Improvement Score (AIS), which accounts for improvement as well as worsening GC-toxicity.1 In The Lancet Rheumatology, Naomi Patel and colleagues3 present an analysis of domain scores of the GTI using data from the phase 3 ADVOCATE trial.4 In a clinical trial context where the GTI is used to produce repeated measures to demonstrate differences between (and within) groups of patients taking different dosages of glucocorticoids, and to measure the impact of steroid sparing agents, it is expected to have a high level of measurement validity and reliability
