C4A and Venous thrombosis: Using thrombosis as a response, multiple logistic regression analyses suggested that higher plasma C4 protein levels and the presence of lupus anticoagulant (LAC) were among the strongest independent biomarkers associated with thrombosis (C4, p = 6.2 × 10−9; LAC, p = 6.9 × 10−5) (Supplementary Table).