Objective To determine cutoff values for defining the state of high disease activity (HDA) in juvenile idiopathic arthritis (JIA) using the Juvenile Arthritis Disease Activity Score (JADAS).

Methods For the selection of cutoff values, data from a clinical database including 609 patients were used. Optimal cutoff values were determined against external criteria by calculating the 25th and 10th centile of cumulative score distribution and through receiver operating characteristic curve analysis. External criteria were based on the therapeutic decision made by the attending doctor. Cross-validation was performed using five patient samples that included 1421 patients.

Results The optimal cutoff values were those obtained through the 90% fixed sensitivity method. The selected JADAS cutoff values were the following: 4.2 and 8.5 for JADAS27 in oligoarthritis and polyarthritis, respectively; 4.2 and 10.5 for both JADAS10 and JADAS71 in oligoarthritis and polyarthritis, respectively. In cross-validation analyses, the cutoff values showed strong ability to discriminate between different levels of American College of Rheumatology paediatric response in two clinical trials and could predict worse functional and radiographic outcome.

Conclusions Cutoff values for classifying HDA in JIA using the JADAS were developed. In cross-validation analyses, they proved to have good construct and discriminant validity and ability to predict disease outcome.