Validation and important differences for the Sarcoidosis Assessment Tool. A new patient-reported outcome measure

Rationale: Patient-reported outcome (PRO) measures have been developed to measure symptoms and other aspects of health-related quality of life.

Objectives: The Sarcoidosis Assessment Tool (SAT), a sarcoidosis-specific PRO, was administered in a lung and skin sarcoidosis treatment trial. We explored SAT performance characteristics and correlation with standard clinical measurements to validate it as a useful clinical sarcoidosis-specific PRO.

Methods: The SAT analyses focused on baseline and Week 16 assessments. Besides the SAT, participants underwent clinical and physician assessments plus additional PROs that were used as anchor variables and were compared with the SAT. Reliability was evaluated by using Cronbach α coefficient. Spearman correlation coefficients were used to evaluate the association between SAT scores with clinical and other PRO measures. Changes between assessments in the clinical and PRO "anchor" variables were classified as improved, stable, or worsened. Mean differences between adjacent categories of the known groups and mean changes from the ability to detect change analyses were reviewed for appropriate clinically important difference estimates.

Measurements and main results: Results from 173 patients were analyzed. Each SAT module reflected appropriate anchor variables at baseline and in terms of change. The Cronbach α for each of these modules was at least 0.87. In addition, we successfully established a clinically important difference range for each SAT module.

Conclusions: We demonstrated that the SAT is a reliable and consistent sarcoidosis-specific PRO. It has excellent internal consistency and reliability. A range of clinically important differences has been established for the SAT modules. Clinical trial registered with www.clinicaltrials.gov (NCT 00955279).