Background Cystatin C (CysC) is produced at a constant rate by all nucleated cells. It is freely filtered by the renal glomeruli and reabsorbed and catabolized in the proximal renal tubules. Compared with serum creatinine level, serum CysC concentration is not affected by gender and muscle mass, and therefore provides a more accurate measure of glomerular filtration rate (GFR). Patients with systemic lupus erythematosus (SLE) often develop glomerulonephritis and their quality of life and prognosis are impaired. Anti-DNA antibody and serum compliments are used as serum markers of developing renal damage. CysC can be used for early detection of renal damage. Moreover, CysC may be associated with inflammation in SLE1.
Objectives To examine whether CysC correlates with SLE disease activity.
Methods Fifty-two patients with SLE (50 women and 2 men) who visited our hospital from Jun. 2012 to Apr. 2013 were enrolled. Mean age (SD) was 47.9 (13.2) years. Median (range) of SLEDAI was 2 (0-35). Average dose of steroid (prednisone equivalent) was 7.4 mg/day. Blood samples were collected and serum creatinine, adjusted calcium concentration, levels of C3 and C4, anti-DNA antibody titers, TSH, free T4, matrix metalloproteinase-3 (MMP-3), and 25-OH vitamin D were examined. Stepwise regression was used for multivariate analysis to test which factors correlated with CysC. GFR was estimated by MDRD method.
Results CysC correlated with creatinine, MMP-3, free T4, and SLEDAI scores. Of 52 patients, 10 had abnormal GFR (<60 ml/min) and all of them showed elevated CysC levels (>0.9 mg/L). Forty-two patients with normal GFR were divided into high level of CysC (n=23) and normal level of CysC (n=19). Patients with normal GFR and high CysC showed significantly higher titers of ant-DNA antibody and higher score of SLEDAI than those with normal GFR and normal CysC.
Conclusions Thyroid function affects GFR2 and serum MMP-3 lever is closely associated with clinical features relevant to lupus nephritis3. Besides creatinine and these renal associated factors, CysC independently correlated with SLEDAI. Moreover, Patients with normal GFR had high titers of anti-DNA antibody and high scores of SLEDAI if their CysC levels elevated, which suggests CysC associates with SLE disease activity independent of renal function.
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Disclosure of Interest None declared