In 1985 the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) was first developed to measure disease activity in SLE patients in the previous 10 days.

In 2002 a revised version of SLEDAI, SLEDAI 2000 (SLEDAI-2K), was introduced which allows the scoring of the persistent active disease. SLEDAI-2K was validated against the original SLEDAI and shown to describe disease activity at various activity levels in a comparable manner to the original SLEDAI.

SLEDAI and its modification document descriptors present at the time of the visit or the preceding 10 days.

In 2010 SLEDAI-2K 30 days was validated against SLEDAI-2K 10 days to describe disease activity over the previous 30 days.

S2K RI-50 is a reliable and valid index able to demonstrate incomplete but clinically significant ≥50% improvement in disease activity in lupus patients.

The S2K RI-50 comprises the same 24 descriptors, covering 9 organ-systems, and reflecting disease activity over the previous 30 days as in SLEDAI-2K 30 days.

The S2K RI-50 data retrieval form standardizes the documentation of the descriptors.