Development and initial validation of the systemic lupus erythematosus disease activity index 2000 responder index 50

To describe the development and validation of the Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K) Responder Index 50 (SRI-50), an index to measure improvement in disease manifestations on followup visits.

We proposed 50% improvement of SLEDAI-2K scores as this was felt by clinicians to reflect a clinically important improvement. We determined the best definitions of 50% improvement in each of the SLEDAI-2K descriptors. The SRI-50 data retrieval form was developed to standardize the documentation of the descriptors. The new assigned scores for the descriptors of SRI-50 were derived by dividing the score of SLEDAI-2K by 2. To evaluate the construct validity of SRI-50, all patients attending the Lupus Clinic from September 2009 to December 2009 were studied. Patients were assessed initially and on a followup visit according to both SLEDAI-2K and SRI-50 along with physician response assessment on a Likert scale (LS), which was considered the external construct.

SRI-50 is a 2-page document comprising 24 descriptors. The scoring method is simple, intuitive, and cumulative, and can be derived during the patient visit. Of the 298 patients enrolled in this study, 141 had a followup visit and were studied further. SRI-50 scores decreased more in patients with LS ≥ 50% compared to LS < 50% with a decrease of > 3. The decrease in SRI-50 scores was statistically and clinically more significant than the decrease in SLEDAI-2K scores. SRI-50 detected incomplete improvement, which would not have been discerned using SLEDAI-2K.

SRI-50 has construct validity and is able to demonstrate incomplete, but clinically significant, improvement in disease activity between visits in patients with lupus.