C3 and streptococcal infection: Some factors have been reported to be associated with renal involvement in IgA vasculitis, such as age more than 10-years at onset, male gender, digestive tract symptoms, persistency (> one month) or recurrence of purpura, white blood cell (WBC) count>15X109/L, platelet count >500X109/L, lymphopenia, upper respiratory tract infection, especially streptococcal infection with elevated Anti Streptolysin-O (ASO) titer, and decreased C3 level (4, 6).