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This article is part of the supplement: Lupus 2012: New targets, new approaches

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Development validation and reliability of the Systemic Lupus Erythematosus Disease Activity Index 2000 Responder Index-50

Z Touma*, DD Gladman and MB Urowitz

  • * Corresponding author: Z Touma

Author Affiliations

University of Toronto, ON, Canada

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Arthritis Research & Therapy 2012, 14(Suppl 3):A55  doi:10.1186/ar3989

The electronic version of this article is the complete one and can be found online at:

Published:27 September 2012

© 2012 Touma et al.; licensee BioMed Central Ltd.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K) is a global disease activity index composed of 24 descriptors reflecting nine organ systems. The SLEDAI-2K measures only complete recovery in active descriptors on follow-up visits. Thus, an improvement in the SLEDAI-2K descriptors is captured when a manifestation has completely resolved. The aims were: to develop and validate an outcome measure, the SLEDAI-2K Responder Index-50 (S2K RI-50), able to capture partial improvement, ≥50%, in each of the active descriptors at subsequent visits; to test the reliability of S2K RI-50; and to evaluate S2K RI-50 sensitivity to response at 6 and 12 months.


The S2K RI-50 was constructed based on SLEDAI-2K. New definitions for all descriptors were generated along with criteria to identify 50% improvement. The S2K RI-50 Data Retrieval Form standardizes the documentation of the descriptors. From September 2009 to April 2011, all lupus patients seen at the Lupus Clinic were assessed at baseline and follow-up visits using SLEDAI-2K, S2K RI-50 and physician global assessment (visual analog scale online and Likert scale). Concurrent construct validity: correlation of the S2K RI-50 was determined using the Likert scale as the external construct. Inter-rater/intra-rater reliability (intraclass correlation coefficient (ICC)): 40 patient scenarios with baseline and follow-up visits derived from real patients were developed. Ten rheumatologists scored the profiles with the SLEDAI-2K and S2K RI-50, on two occasions 2 weeks apart. Sensitivity to response: responders using the SLEDAI-2K, S2K RI-50 and SLE Responder Index (SRI) were identified at 6 and 12 months among 103 consecutive active patients. Patients defined as S2K RI-50 responders were compared with SRI responders; considered the gold standard.


The S2K RI-50 and its Data Retrieval Form were developed. The initial validation on 141 patients showed that S2K RI-50 has construct validity (correlated with Likert scale; r = 0.48; P < 0.0001). The S2K RI-50 is reliable and the ICC for inter-rater/intra-rater ranged from 0.86 to 1.00. The percentage of responders at 6 and 12 months was 44% and 51% by SLEDAI-2K and 43% and 51% by SRI respectively. The percentage of S2K RI-50 responders at 6 and 12 months was higher at 51% and 58% respectively.


The S2K RI-50 is novel valid and reliable responder index able to identify patients with partial, ≥50% improvement. The S2K RI-50 identified more responders as compared with the SLEDAI-2K and SRI at the 6 and 12 month period. The S2K RI-50 can be used independently to identify patients with clinically important improvement.


The authors acknowledge all who participated in these studies.