ELISA analysis of urine ferritin and its correlation with disease activity, urine protein/Cr levels, and complement levels. Ferritin levels in urine of healthy (N = 9), inactive SLE (N = 10), and active SLE (N = 17) patients were determined by ELISA (Raybiotech, Norcross, GA, USA). Expression of ferritin in the urine of active SLE patients were increased 12-fold as compared to healthy controls (P < 0.001), and by 3-fold as compared to inactive SLE patients (P = 0.02). Ferritin expression was 4-fold higher in inactive SLE patients as compared to healthy controls (P = 0.03). Data represent the mean ± SEM. Urine ferritin/Cr levels correlated significantly with urine protein/Cr levels (R = 0.43, P = 0.013), with SLEDAI (R = 0.25, P = 0.096), and with serum C3/C4 levels (R = 0.301, P = 0.067).