OBJECTIVE: To standardize outcome measures in systemic lupus erythematosus 
(SLE). Three indices were identified which could adequately describe outcome 
(disease activity, damage from disease, and health status); we describe here the 
development of the Disease Activity Index.
METHODS: Twenty-four variables were identified as important factors in a disease 
activity index. These were used to generate 574 patient profiles, which were 
rated on a disease activity scale of 0-10 by 14 rheumatologists. A second rating 
of 10 of the profiles yielded scores that were not significantly different from 
the first, indicating that experienced clinicians can reliably make global 
estimates of disease activity. Multiple regression models were used to estimate 
the relative importance of the 24 clinical variables in the physicians' global 
rating of disease activity. These were estimated on a "training set" of 75% of 
physicians' ratings, and then validated on a "testing set," consisting of the 
remaining 25% of physicians' ratings.
RESULTS: The explanatory power of the models in the training set was high (R2 = 
0.93). The models' regression coefficients for the organ systems were simplified 
for easier use in clinical practice. This generated a "weighted" index of 9 
organ systems for disease activity in SLE, the SLEDAI, as follows: 8 for central 
nervous system and vascular, 4 for renal and musculoskeletal, 2 for serosal, 
dermal, immunologic, and 1 for constitutional and hematologic. The maximum 
theoretical score is 105, but in practice, few patients have scores greater than 
45. The SLEDAI predicted well the physicians' ratings in the testing set 
(Pearson's correlation coefficients = 0.64-0.79).
CONCLUSION: The SLEDAI is a validated model of experienced clinicians' global 
assessments of disease activity in lupus. It represents the consensus of a group 
of experts in the field of lupus research.