C4A and Venous thrombosis: Among these four groups, significantly higher mean protein levels were observed for patients with thrombosis only than with SLE only for plasma protein levels of total C4 (p = 2.2 × 10−9), C4A (p = 1.9 × 10−6), C4B (p = 1.3 × 10−6), C3, (p = 2.6 × 10−5), ACLA-IgG (p = 1.2 × 10−5), and in female to male ratio sex ratio (p = 1.6 × 10−6).