OBJECTIVE: To compare the responsiveness of BILAG-2004 and SLEDAI-2000 disease activity indices and determine if there was any added value in combining BILAG-2004, BILAG System Tally (BST) or simplified BST (sBST) with SLEDAI-2000.
METHODS: This was a multi-centre longitudinal study of SLE patients. Data were collected on BILAG-2004, SLEDAI-2000 and therapy on consecutive assessments in routine practice. The external responsiveness of the indices was assessed by determining the relationship between change in disease activity and change in therapy between two consecutive visits. Comparison of indices and their derivatives was performed by assessing the main effects of the indices using logistic regression. ROC curves analysis was used to describe the performance of these indices individually and in various combinations and comparisons of AUC were performed.
RESULTS: There were 1414 observations from 347 patients. Both BILAG-2004 and SLEDAI-2000 maintained an independent relationship with change in therapy when compared. There was some improvement in responsiveness when continuous SLEDAI-2000 variables (change in score and score of previous visit) were combined with BILAG-2004 system scores. Dichotomisation of BILAG-2004 or SLEDAI-2000 resulted in poorer performance. BST and sBST had similar responsiveness as the combination of SLEDAI-2000 variables and BILAG-2004 system scores. There was little benefit in combining SLEDAI-2000 with BST or sBST.
CONCLUSIONS: The BILAG-2004 index had comparable responsiveness to SLEDAI-2000. There was some benefit in combining both indices. Dichotomisation of BILAG-2004 and SLEDAI-2000 leads to suboptimal performance. BST and sBST performed well on their own; sBST is recommended for its simplicity and clinical meaningfulness.