FURTHER VALIDATION OF THE BILAG DISEASE-ACTIVITY INDEX IN PATIENTS WITH SYSTEMIC LUPUS-ERYTHEMATOSUS

Objective-To examine the association among the BILAG disease activity index components and their relations with global assessments, health s tatus, and laboratory tests with regard to the validity of the BILAG i ndex. Methods-A cross sectional study of consecutive patients with sys temic lupus erythematosus (SLE) attending a specialist lupus outpatien t clinic between July 1994 and February 1995. The internal consistency of the British Isles Lupus Assessment Group (BILAG) index-a disease a ctivity assessment system for SLE patients, based on the principle of the physician's intention to treat-was examined using Cronbach's coeff icient alpha. The association of the components of the BILAG index wit h health status as measured with the MOS Short Form 20 (SF-20), with p atients) and doctors' global assessments of patient wellbeing and with laboratory tests was analysed with Spearman rank correlations. Result s-133 female and eight male patients, age 20.1 to 88.7 years (mean 41. 1, SD 12.5), were included. With few exceptions, the components of the BILAG index which reflect disease activity in different organ systems were not associated with each other. With the exception of the mucocu taneous component, we found a significant relation between all compone nts of BILAG and global assessment of patient wellbeing, health status , erythrocyte sedimentation rate, or serum C3 level. Conclusions-The s tudy confirms the validity of all but the mucocutaneous component of t he BILAG index. However, disease activity in different organ systems i n SLE does not follow a common pattern. Thus the individual BILAG comp onents should be used rather than the total BILAG score as a primary e ndpoint in clinical and epidemiological studies. To capture the total effect of SLE on an individual measures of disease activity, damage, a nd health status are all needed.