Background and aims To investigate relationship between cystatin C (Cys)/creatinine ratio and disease activity of systemic lupus erythematosus (SLE).

Methods Clinical and laboratory data were collected from 52 patients with SLE who had been examined their Cys at least once. Female rate was 96.2% and the average age±standard deviation was 47.9±13.2 years old. Estimated GFR (eGFR) was calculated based on Cys (eGFRcys) and creatinine (eGFRcre). Shrunken pore syndrome (SPS) was defined as eGFRcys/eGFRcre <60%.

Results Comparing 20 patients with Cys <1.2 mg/L and 32 patients with Cys <1.2 mg/L, SLE disease activity index (SLEDAI) was significantly higher in the former group than in the latter group (7.7±7.8 vs. 2.8±4.0, p<0.01), while the dose of corticosteroids did not differ significantly. The ratio of Cys (mg/L) to creatinine (mg/dl) was significantly higher in 25 patients with SLEDAI ≥3 than in 27 patients with SLEDAI <3 (1.99±0.45 vs. 1.68±0.35, p<0.01). SLEDAI was significantly higher in 8 patients with SPS than in 44 patients without SPS (10.6±10.9 vs. 3.6±4.3, p<0.01). Organ involvement was found in 87.5% of SPS (2 with retinopathy, 1with cerebral haemorrhage, 1 with myositis plus nephritis, 1 with hemolytic anaemia, 1 with pleuritis, and 1 with enteritis), while 33 patients (75.0%) without SPS were in stable state.

Conclusions SLE patients with increased ratio of Cys to creatinine had high disease activity, and organ involvements were found with high frequency in patients with SPS.