Extensive analyses of gene copy number variations for total C4, C4A, and C4B, plasma protein levels of total C4, C4A, C4B, C3, factor H and MBL, and antiphospholipid antibodies revealed distinct patterns of diversity that can be relevant and effective quantitative biomarkers for thrombosis, SLE and recurrent pregnancy loss. This evidence concerns the gene C4A and Venous thrombosis.