Response to: ‘SLE-DAS: ready for routine use’ by Mathew et al

It was with great interest that we read the letter ‘SLE-DAS: Ready for routine use?’ by Mathew and coauthors.1 Mathew et al commented on our recent article reporting the derivation and validation of the Systemic Lupus Erythematosus Disease Activity Score (SLE-DAS),2 which demonstrated a much higher sensitivity to change of SLE disease activity, as compared with SLE Disease Activity Index 2000 (SLEDAI-2K). Mathew et al ’s main concern is in regard of the SLE-DAS scoring of active lupus nephritis (LN). The SLE-DAS renal component is measured continuously, applying a logarithmic scale of proteinuria absolute value (to be scored only if above 500 mg/day and provided it is attributable to active LN). This is very different of the SLEDAI-2K renal component that comprises four dichotomous variables (proteinuria above 500 mg/day, pyuria, haematuria and urinary casts, each one scored solely as present or absent with a weight of 4 points if present and regardless of severity).3 In the derivation of the SLE-DAS, we modelled the renal component using longitudinal data of real patients with active LN from a large, well-characterised tertiary lupus cohort.4 5 The SLE-DAS with its continuous scoring of the absolute value of proteinuria amends risks of major bias of SLEDAI-2K regarding renal involvement. In patients with active LN, the …