Objective To explore the serum level of complement 1q(C1q) in systemic lupus erythematosus patients and to analyze its significance in diagnosis and prognosis of systemic lupus erythematosus with lupus flare and lupus nephritis(LN). Methods According to the clinical data, 150 cases of subjects were divided into four groups. There were 60 cases in SLE group, 30 cases in other rheumatic disease group, 30 cases in other kidney disease group and 30 cases in normal control group. The SLE group contained 33 cases...