Derivation of an Appropriate Outcome Measure in Lupus

Aim: To develop an outcome measure to identify “responders” for patients who had a clinically important improvement in lupus disease activity with treatment. Methods: The outcome measure derived was based on the commonly used disease activity measure SLEDAI-2K which documents findings over the previous 10 days. Since patients in drug trials are followed at monthly intervals it was necessary to validate SLEDAI-2K 30 days against SLEDAI-2K 10 days. Two prospective studies were accomplished for this purpose. SLEDAI-2K 30 days was used to develop the new responder index, SLEDAI-2K Responder Index-50 (SRI-50). The SRI-50 data retrieval form was developed to standardize the documentation of the descriptors. The construct validity of SRI-50 was prospectively evaluated against an external construct. The reliability of SRI-50 was tested in a multi-centre study. A retrospective analysis over 10 years was used to further validate SRI-50. SRI-50 ability to enhance the SLE Responder Index (SRI) in detecting “responders” was evaluated. The performance of SRI-50 was investigated against SLEDAI-2K and SRI over 12 months. Results: SLEDAI-2K 30 days was validated to describe disease activity over the previous 30 days. The responder index to SLEDAI-2K, SRI-50 was developed including the SRI-50 Definitions and SRI-50 Data Retrieval Forms. The initial validation of SRI-50 confirmed its construct validity to identify ≥ 50 % improvement. SRI-50 is reliable and can be used by both rheumatologists and trainees. The retrospective analysis confirmed that SRI-50 is valid in identifying ≥ 50 % improvement in an efficient time. SRI-50 enhances the performance of SRI and identifies more “responders” than SLEDAI-2K and SRI at 6 and 12 months. Conclusions: SRI-50, is a valid and reliable responder index to identify patients with partial, ≥50% improvement in disease activity in an efficient time. SRI-50 can be used as an independent outcome measure of improvement in patients with SLE.Ph