Complement activation is associated with autoimmune disease activity[47, 48] and emerging evidence has shown low levels of C3 and C4 in patients with PAPS with thrombosis and poor pregnancy outcomes.[49, 50] Consistent with these findings, we found that aPL‐positive patients with PAPS have lower C3, C4, and PLT levels. Here, C3 is linked to Venous thrombosis.