The BILAG2004-Pregnancy Index is a valid disease activity outcome measure for pregnant SLE patients

OBJECTIVES: This study was to determine whether the BILAG2004-Pregnancy Index (BILAG2004-P) has construct/criterion validity and is sensitive to change. METHODS: This was an observational multicentre study that recruited pregnant SLE patients. Data were collected on disease activity [using the BILAG2004-P and Physician Global Assessment (PGA)], investigations and therapy at each assessment. The overall BILAG2004-P score as determined by the highest score achieved by any system was used in the analysis. Cross-sectional analysis was used for construct and criterion validity. The comparison was with C3, C4 and anti-dsDNA for construct validity, while it was with change in therapy and PGA in criterion validity. Sensitivity to change was assessed by determining the relationship between the change in BILAG2004-P and the change in therapy between two consecutive visits. RESULTS: A total of 97 patients with 112 pregnancies were recruited. There were 610 assessments available for construct/criterion validity analysis (98.2% of pregnancies had more than one assessment) and 497 observations for sensitivity to change analysis. Increasing BILAG2004-P scores were associated with low C3. The active BILAG2004-P score (grade A or B) was associated with an increase in therapy and the PGA of active disease. There was an increasing likelihood of higher overall scores with an increase in therapy and the PGA of active disease. In the sensitivity to change analysis, an increase in the BILAG2004-P score was associated with an increase in therapy and inversely associated with a decrease in therapy. A decrease in the BILAG2004-P score was associated with a decrease in therapy and inversely associated with an increase in therapy. CONCLUSION: The BILAG2004-P has criterion validity and is sensitive to change.